Agate: Difference between revisions

Latest revision as of 22:25, 19 November 2025

Template:Short description Script error: No such module "other uses". Template:Good article Template:Infobox mineral

Agate (Template:IPAc-en Template:Respell) is a variously translucent, banded variety of chalcedony. Agate stones are characterized by alternating bands of different colored chalcedony and may also include visible quartz crystals. They are common in nature and can be found globally in a large number of different varieties. There are some varieties of chalcedony without bands that are commonly called agate (moss agate, fire agate, etc.); however, these are not true agates. Moreover, not every banded chalcedony is an agate; for example, banded chert forms via different processes and is opaque. Agates primarily form as nodules within volcanic rock, but they can also form in veins or silicified fossils. Agate has been popular as a gemstone in jewelry for thousands of years, and today it is also popular as a collector's stone. Some duller agates sold commercially are artificially treated to enhance their color.

Etymology

Agate was given its name by Theophrastus, a Greek philosopher and naturalist. He discovered the stone Template:Circa along the shoreline of the River Achates (Template:Langx), now the Dirillo River, on the Italian island of Sicily, which at the time was a Greek territory.^[1]Template:Rp

Composition

Agate is composed principally of chalcedony,^[2] a microscopic (microcrystalline) and submicroscopic (cryptocrystalline) form of quartz that grows in fibers. The chemical composition of quartz is Template:Chem2, also known as silica. Normally, between 1% and 20% of the "quartz" in chalcedony is actually moganite, a quartz polymorph.^[3] Unlike macroscopic (macrocrystalline) quartz, which is anhydrous, chalcedony normally contains very small amounts of water bound to its crystal structure.^[3]^[1]Template:Rp

Agate contains multiple layers, or bands, of chalcedony fibers.^[2] The fibers are twisted,^[4]^[1]Template:Rp forming a helical shape.^[5] There are two different types of chalcedony fibers: length-slow (also known as quartzine) and length-fast. Agate primarily contains length-fast chalcedony fibers, consisting of crystals stacked perpendicular to the c-axis (side to side). Some intergrown quartzine may also be present, consisting of quartz crystals stacked parallel to the c-axis (tip to tip).^[3]

Agate can sometimes contain small amounts of opal, an amorphous, hydrated form of silica.^[1]Template:Rp Agates also frequently contain macrocrystalline quartz, particularly in the center.^[6]^[1]Template:Rp

Formation

File:Agate- & quartz-lined geode 5 (32375570960).jpg

Agate geode

Geologists generally understand the early stages of agate formation, but the specific processes that result in band development are widely debated. Since they form in cavities within host rock, agate formation cannot be directly observed,^[6] and agate banding has never been successfully replicated in the lab.^[5]^[7]

Script error: No such module "anchor".Agates are most commonly found as nodules within the cavities of volcanic rocks^[8] such as basalt, andesite, and rhyolite. These cavities, called vesicles (amygdaloids when filled),^[1]Template:Rp are gas bubbles that were trapped inside the lava when it cooled.^[8]^[6]^[1]Template:Rp The vesicles are later filled with hot, silica-rich water from the surrounding environment, forming a silica gel. This gel crystallizes through a complex process to form agates.^[1]Template:Rp Since agates usually form in lavas poor in free silica, there are multiple theories of where the silica originates from, including micro-shards of silica glass from volcanic ash or tuff deposits and decomposing plant or animal matter.^[1]Template:Rp Agates are much harder than the rocks they form in; some varieties (e.g. Lake Superior agates) are frequently found detached from their host rock.^[1]Template:Rp

Script error: No such module "anchor".In wall-banded agates, chalcedony fibers grow radially from the vesicle walls inward, perpendicular to the direction of the bands.^[2]^[9] The vesicle walls are often coated with thin layers of celadonite or chlorite,^[6]^[1]Template:Rp soft, green phyllosilicate minerals that form from the reaction of hot, silica-rich water with the rock.^[6] This coating provides a rough surface for the chalcedony fibers to form on, initially as radial spherulites. The rough surface also causes agate husks to have a pitted appearance once the coating has been weathered away or removed.^[1]Template:Rp Sometimes, the spherulites grow around mineral inclusions, resulting in eyes, tubes, and sagenitic agates.^[2]

The first layer of spherulitic chalcedony is typically clear, followed by successive growth bands of chalcedony alternated with chemically precipitated color bands, primarily iron oxides.^[1]Template:Rp The center is often macrocrystalline quartz,^[6] which can also occur in bands and possibly forms when there is not enough chemically bound water in the silica gel to promote chalcedony polymerization.^[1]Template:Rp When the silica concentration of the gel is too low, a hollow center forms, called an agate geode. In geodes, quartz forms crystals around the cavity, with the apex of each crystal pointing towards the center. Occasionally, quartz in agates may be colored, occurring in varieties such as amethyst or smoky quartz.^[1]Template:Rp

Script error: No such module "anchor".Level-banded agates form when chalcedony precipitates out of solution in the direction of gravity, resulting in horizontal layers of microscopic chalcedony spherulites.^[2] Level banding commonly occurs together with wall banding, often forming at the base of the vesicle or in the center when the gel stops adhering to the vesicle walls. This is probably due to a decrease in bound water in the gel. Level-banded agate is less dense and less compact than wall-banded agate, as it is less fibrous and more granular.^[1]Template:Rp

Enhydro agates, or enhydros, form when liquid water becomes trapped within an agate (or chalcedony) nodule or geode, often long after its formation.^[10]^[11]

Script error: No such module "anchor".Agates can also form within rock fissures, called veins.^[1]Template:Rp Vein agates form in a manner similar to nodular agates (see above),^[1]Template:Rp and they include lace agates such as blue lace agate and crazy lace agate. Veins may form in either volcanic rock or sedimentary rock.^[1]Template:Rp

Less commonly, agates can form as nodules within sedimentary rocks such as limestone, dolomite or tuff. These agates form when silica replaces another mineral, or silica-rich water fills cavities left by decomposed plant or animal matter.^[1]Template:Rp Script error: No such module "anchor".Sedimentary agates also include fossil agates, which form when silica replaces the original composition of an organic material.^[12] This process is called silicification, a form of petrification. Examples include petrified wood,^[13] agatized coral,^[14] and Turritella agate (Elimia tenera).^[15] Although these fossils are often referred to as being "agatized", they are only true agates if they contain bands.^[2]

Structural varieties

Agates are broadly separated into two categories based on the type of banding they exhibit.^[16]^[1]Template:Rp Wall banding, also called concentric banding or adhesional banding, occurs when agate bands follow the shape of the cavity they formed in. Level banding, also called water-level banding, gravitational banding, horizontal banding, parallel banding, or Uruguay-type banding, occurs when agate bands form in straight, parallel lines. Level banding is less common and usually occurs together with wall banding.^[2]

File:Agate 6 (32375570980).jpg

Agate exhibiting wall banding (top) and level banding (bottom)

Wall-banded agates

Script error: No such module "anchor".Fortification agates are any wall-banded agates with tight, well-defined bands.^[1]Template:Rp They get their name from their appearance which resembles the walls of a fort. Fortification agates are one the most common varieties, and they are what most people think of when they hear the word "agate".^[17]

Script error: No such module "anchor".Lace agates exhibit a lace-like pattern of bands with many swirls, eyes, bends, and zigzags. Unlike most agates, they usually form in veins instead of nodules.^[1]Template:Rp

Script error: No such module "anchor".Faulted agates have bands that were broken and slightly shifted by rock movement and then re-cemented together by chalcedony. They have the appearance of rock layers with fault lines running through them. Brecciated agates also have bands that were broken apart and re-cemented with chalcedony, but they consist of disjointed band fragments at random angles.^[18]^[1]Template:Rp They are a form of breccia, which is a textural term for any rock composed of angular fragments.^[18]^[19]

Script error: No such module "anchor".Eye agates have one or more circular, concentric rings on their surface.^[20] These "eyes" are actually hemispheres that form on the husk of the agate and extend inward like a bowl.^[21]

Script error: No such module "anchor".Sagenitic agates, or sagenites, have acicular (needle-shaped) inclusions of another mineral, usually anhydrite, aragonite, goethite, rutile, or a zeolite. Chalcedony often forms tubes around these crystals and may eventually replace the original mineral, resulting in a pseudomorph.^[1]Template:Rp The term "sagenite" was originally a name for a type of rutile, and later rutilated quartz. It has since been used to describe any quartz variety with acicular inclusions of any mineral.^[22]

Script error: No such module "anchor".Tube agates contain tunnel-like structures that extend all the way through the agate.^[23] These "tubes" may sometimes be banded or hollow, or both. Tube agates form when chalcedony grew around sagenitic inclusions embedded within the agate, forming stalactitic structures. Visible "eyes" can also appear on the surface of tube agates if a cut is made (or the agate is weathered) perpendicular to the stalactitic structure.^[1]Template:Rp

Script error: No such module "anchor".Dendritic agates have dark-colored, fern-like patterns (dendrites) that form on the surface or in the spaces between bands.^[24]^[1]Template:Rp They are composed of manganese or iron oxides. Moss agates exhibit a moss-like pattern and are usually green or brown in color. They form when dendritic structures on the surface of an agate are pushed inward with the silica gel during their formation. Moss agate was once believed to be petrified moss, until it was discovered the moss-like formations are actually composed of celadonite, hornblende, or a chlorite mineral. Plume agates are a type of moss agate, but the dendritic "plumes" form tree-like structures within the agate. They are often bright red (from inclusions of hematite) or bright yellow (from inclusions of goethite).^[1]Template:Rp While dendrites frequently occur in banded agates, moss and plume agates usually lack bands altogether. Therefore, they are not true agates according to the mineralogical definition.^[2]^[25]

Script error: No such module "anchor".Iris agates have bands that are fine enough that when thinly sliced, they cause white light to be diffracted into its spectral colors. This "iris effect" usually occurs in colorless agates, but it can also occur in brightly colored ones.^[1]Template:Rp

Brazilian agate with classic fortification banding

Brazilian agate with classic fortification banding
Tumbled Lake Superior eye agates

Tumbled Lake Superior eye agates
Dendritic agate from India

Dendritic agate from India
Moss agate cabochons

Moss agate cabochons
Iris agate from petrified wood

Iris agate from petrified wood

Level-banded agates

Agates with level banding are traditionally called onyx, although the formal definition of the term onyx refers to color pattern, not the shape of the bands.^[26] Accordingly, the name onyx is also used for wall-banded agates. Onyx is also frequently misused as a name for banded calcite. The name originates from the Greek word for the human nail, which has parallel ridges.^[1]Template:Rp Typically, onyx bands alternate between black and white or other light and dark colors. Sardonyx is a variety with red-to-brown bands alternated with either white or black bands.^[27]

Thunder eggs are frequently level-banded, however they may also have wall banding. Level banding is also common in Lake Superior agates.^[16]

Onyx agate

Onyx agate
Level-banded thunder egg from Oregon, USA

Level-banded thunder egg from Oregon, USA

Regional varieties

Agates are very common, and they have been found on every continent,^[1]Template:Rp including Antarctica.^[28] In addition to the structural varieties detailed in the previous section, numerous geological, local, and trade names are used to describe agates from different localities.^[1]Template:Rp Below is a table of agate varieties from different regions of the world.Template:Sticky header

Regional varieties of agate
Name	Locality	Region	Description	Type	Geologic environment	Age	Photo(s)	References
Blue lace agate	Namibia	Africa	Pale blue and white lace agate	Vein agate	Volcanic rock (dolomite associated with dolerite)		File:Blue Lace Agate.jpg Blue lace agate from Ysterputz Mine, Namibia	^[1]Template:Rp
Script error: No such module "anchor".Botswana agate	Botswana	Africa	Typically Template:Convert in diameter, with contrasting bands of purple, pink, black, grey, and white	Nodular agate	Volcanic rock (Karoo Series, basalt)	Permian period	File:Agat - Bobonong, Botswana.jpg Botswana agate	^[1]Template:Rp
Script error: No such module "anchor".Malawi agate	Malawi	Africa	Typically bright red or orange with contrasting white bands, some are pink and blue	Nodular agate	Volcanic rock	Permian period		^[1]Template:Rp
(Unnamed agate)	Bellingshausen Station, King George Island	Antarctica	White and clear bands	Nodular agate			File:Agate (Tertiary; Agate Bay, King George Island, South Shetland Islands) 1.jpg Agate from King George Island, Antarctica	^[28]
Script error: No such module "anchor".Queensland agate	Queensland	Australia	Often green or yellow-green (colors that are rarely found in other regions), frequently level-banded	Nodular agate	Volcanic rock (basaltic lava flows)	Late Permian period	File:Agat ze strefą krustalną - Agate Creek, Queensland, Australia.jpg Queensland agate with level banding	^[1]Template:Rp
German agate	Near Idar-Oberstein, Germany	Europe	Often red or pink, sometimes other colors	Nodular agate	Volcanic rock	Permian period	File:Agate-MCG 91225-P4150832-white.jpg German agate from Idar-Oberstein	^[1]Template:Rp
Scottish agate	Stonehaven to just south of Ayr, near Oban, and surrounding the Cheviot Hills, Scotland, United Kingdom	Europe	Various colored bands	Nodular agate	Volcanic rock (andesite)	Early Devonian period	File:Agate detail, Scotland 007 (cropped).jpg Close-up of a Scottish agate from Ayrshire	^[1]Template:Rp
Small Isles agate	Islands off the west coast of Scotland, United Kingdom	Europe	Various colored bands	Nodular agate	Volcanic rock (basalt)	Tertiary period		^[1]Template:Rp
Potato stone (Pot stone)	Bristol and Somerset, England, United Kingdom	Europe	Irregularly-shaped, reddish, banded agate nodules, typically surrounding a hollow cavity lined with macroscopic quartz, but sometimes completely filled	Nodular agate	Sedimentary rock (dolomitic conglomerate and marl)	Triassic period	File:Quartz-agate (12250382174).jpg Potato stone from England	^[1]Template:Rp
Script error: No such module "anchor".Boley agate	Central Oklahoma, United States	North America	White fortification and eye banding with clasts of brecciated chert	Vein agate	Sedimentary rock (Boley conglomerate layer, Vamoosa formation)	Virgilian series		^[29]
Script error: No such module "anchor".Coldwater agate (Lake Michigan cloud agate)	Great Lakes Region, United States	North America	Banded lines of grey and white chalcedony	Nodular agate	Sedimentary rock (marine limestone and dolomite)			^[30]
Script error: No such module "anchor".Crazy lace agate	Mexico	North America	Brightly colored lace agate, typically white and red, sometimes yellow and grey	Vein agate	Sedimentary rock	Late Cretaceous period	File:Crazy Lace Agate - Macro Panorama.jpg Crazy lace agate	^[31]^[1]Template:Rp
Script error: No such module "anchor".Dugway geode	Utah, United States	North America	Light grey to blue, often contain hollow cavities lined with drusy quartz	Nodular agate (thunder egg)			File:Dugway Geode (Juab County, Utah, USA) 2 (34581522545).jpg Dugway geode from Utah	^[1]Template:Rp
Fairburn agate	South Dakota and Nebraska, United States	North America	Red fortification banding	Nodular agate	Sedimentary rock (marine carbonate sediments)	Pennsylvanian period	File:Fairburn Agate (ultimately derived from the Minnelusa Formation, Pennsylvanian-Permian; collected east of the Black Hills, western South Dakota, USA) 26 (32406082220).jpg Fairburn agate from western South Dakota	^[32]^[1]Template:Rp
Script error: No such module "anchor".Laguna agate	Ojo Laguna, Chihuahua, Mexico	North America	Vibrant bands in shades of red, orange, pink, or purple, often exhibit parallax or shadow banding, inclusions common	Nodular agate	Volcanic rock (andesite)	Tertiary period	File:LagunaAgateFromMexico.jpg Laguna agate	^[33]^[1]Template:Rp
Lake Superior agate	Near Lake Superior, United States and Canada	North America	Bands in shades of red, orange, yellow, brown, white, and grey, level banding and various structural features common	Nodular agate	Volcanic rock (basalt)	Late Precambrian	File:Agate nodule ("Lake Superior Agate") (floor of Lake Superior, offshore Keweenaw Peninsula, Michigan USA) 2 (33741645898).jpg Rough Lake Superior agate from Keweenaw Peninsula, Michigan	^[34]^[35]^[1]Template:Rp
Script error: No such module "anchor".Lysite agate	Lysite Mountain, Fremont County, Wyoming, United States	North America	Colorful bands with plumes and moss	Vein agate	Sedimentary rock (marine origin)			^[1]Template:Rp
Blue Bed (Pony Butte) thunder egg	Richardson Ranch (formerly Priday Ranch), northeast of Madras, Oregon, United States	North America	Blue and white banding with dark brown shell, frequently level-banded	Nodular agate (thunder egg)	Volcanic rock (John Day Formation, rhyolitic volcanic ash)	Miocene epoch	File:Thunder Egg Agate (Priday Blue Bed, John Day Formation, Miocene; near Madras, Oregon, USA) 3 (33992544563).jpg Blue Bed thunder egg from near Madras, Oregon	^[1]Template:Rp
Script error: No such module "anchor".Holley (Holly) blue agate	Near Holley, Oregon	North America	Lavender to blue	Nodular agate			File:Holley Blue Agate (Linn County, Oregon, USA) 9.jpg Holley blue agate from Oregon	^[1]Template:Rp
Script error: No such module "anchor".Sweetwater agate	Near Sweetwater River, Wyoming	North America	Small moss agates with brown or black dendrites, fluorescent under UV light	Nodular agate	Sedimentary rock (sandstone)	Miocene epoch		^[1]Template:Rp
Turritella agate	Wyoming	North America	Brown fossil agate with the elongated spiral shells of an extinct freshwater snail (Elimia tenera)	Fossil agate	Sedimentary rock (Green River Formation)	Eocene epoch	An irregular dark stone with a flat polished front; many white fragments of elongated, spiral, "corkscrew" shells seem to float in the dark stone Turritella agate (Elimia tenera)	^[15]
Script error: No such module "anchor".Brazilian agate	Rio Grande do Sul and other southeastern states, Brazil	South America	Often large, up to Template:Convert in diameter and over Template:Convert, commonly pale yellow, gray, or colorless (usually sold artificially dyed), are more colorful or contain structural features	Nodular agate	Volcanic rock (decomposed volcanic ash and basalt)	Late Permian period	File:Brazilian agate section (detail).JPG Natural Brazilian agate File:5agat, Brazylia.jpg Dyed Brazilian agate	^[1]Template:Rp
Condor agate	Mendoza, Argentina	South America	Bright red and yellow fortification banding, may contain mossy or sagenitic inclusions	Nodular agate			File:Argentina001.jpg Condor agate	^[1]Template:Rp
Script error: No such module "anchor".Crater agate	Patagonia, Argentina	South America	Typically hollow, black with red bands near the center	Nodular agate	Volcanic rock (rhyolite)	Jurassic period		^[1]Template:Rp
Script error: No such module "anchor".Puma agate	Andes, Patagonia, Argentina	South America	Agatized coral	Fossil agate	Sedimentary rock (marine)			^[1]Template:Rp

Uses

Agate is frequently used as a gemstone in jewelry such as pins, brooches, necklaces, earrings, and bracelets. Agates have also historically been used in the art of hardstone carving to make knives, inkstands, seals, marbles, and other objects. Today, they are widely used to make beads, decorative displays, carvings, and cabochons, as well as face-polished and tumble-polished specimens of varying size and origin. Agate collecting is a popular hobby, and agate specimens can be found in numerous gift shops, museums, galleries, and private collections.^[1]Template:Rp

Industrial uses of agate exploit its hardness, ability to retain a highly polished surface finish and resistance to chemical attack. Historically, it was used to make bearings for highly accurate laboratory balances and mortars and pestles to crush and mix chemicals. During the Second World War, black agate beads mined from Queensland, Australia were used in the turn and bank indicators of military aircraft.^[1]Template:Rp

Agates, particularly moss agates, were first used during the Stone Age to make tools such as arrow and spear points, needles, and hide scrapers. Artifacts from as early as 7000 BCE have been found in Mongolia, and the Natufian people of the Levant are known to have made knives and arrowheads from moss agate as early as 10000 BCE. Agate jewelry from Sumeria has been dated to c. 2500 BCE, and the Ancient Egyptians, Mycenaeans, and Romans all used agate in their jewelry.^[1]Template:Rp Archaeological recovery at the Knossos site on Crete illustrates the role of agates in Bronze Age Minoan culture.^[36] The ornamental use of agate was common in ancient Greece, in assorted jewelry and in the seal stones of Greek warriors.^[37]

Idar-Oberstein was a historically important location in Germany that made use of agate on an industrial scale, dating back to c. 1375 CE.^[1]Template:Rp Originally, locally found agates were used to make all types of objects for the European market, but it became a globalized business around the turn of the 20th century. Idar-Oberstein began to import large quantities of agate from Brazil, as ship's ballast. Making use of a variety of proprietary chemical processes, they produced colored beads that were sold around the globe.^[38]

A Template:Convert barrel full of tumble-polished agate and jasper

A Template:Convert barrel full of tumble-polished agate and jasper
Gold Roman signet ring with portrait of emperor Commodus in niccolo agate, 180-200 CE, found in Tongeren, Gallo-Roman Museum (Tongeren)

Gold Roman signet ring with portrait of emperor Commodus in niccolo agate, 180-200 CE, found in Tongeren, Gallo-Roman Museum (Tongeren)
The "Rubens Vase" (Byzantine Empire). Carved in high relief from a single piece of agate, most likely created in an imperial workshop for a Byzantine emperor.

The "Rubens Vase" (Byzantine Empire). Carved in high relief from a single piece of agate, most likely created in an imperial workshop for a Byzantine emperor.
Victorian banded agate earrings

Victorian banded agate earrings
Patuxent River stone from Maryland — cut and illuminated from behind as a nightlight

Patuxent River stone from Maryland — cut and illuminated from behind as a nightlight
Agate drinking horn, Tang dynasty

Agate drinking horn, Tang dynasty

Treatment and processing

File:Agate, physical properties and origin (Plate VII) BHL48235765.jpg

Composite image of an agate slice showing natural color at the top and various artificial colors below

Many pale or dull agates are artificially treated to enhance their colors and make them more appealing to consumers. Chalcedony is one of the earliest stones to be artificially enhanced,^[39] with heating having been used for centuries to produce the rich red color of carnelian.^[40] Many varieties of chalcedony, including agate, are relatively porous and absorb dyes well.^[39]^[40] The classical methods^[41] of staining agates were developed in the early 19th century in Idar-Oberstein, Germany. After the agates were cut and cleaned, they were soaked for several days in a particular inorganic dye or sugar solution depending on the desired color to be achieved. This was often followed by an acid bath and/or heating ("burning") to oxidize the compounds:^[39]

Blue agates were produced by using a solution of potassium ferricyanide or ferrocyanide followed by iron sulfate, which forms iron ferricyanide (Prussian blue).^[39]
Red agates were produced either by burning alone, or if not enough natural iron was present in the stones, by first soaking them in a solution of iron nitrate and then burning them to form iron oxide.^[39]
Green agates were produced using solutions of nickel or chromium salts followed by burning.^[39]
Black agates were produced by soaking the stones in a sugar solution and then immersing them in sulfuric acid to carbonize the sugars;^[39] brown agates can also be produced using a similar method.^[40]
Yellow agates can be produced using hydrochloric acid followed by burning.^[40]

Organic aniline dyes derived from coal tar began to be used later in the 19th century,^[39] which allowed for the production of agates of additional colors such as pink and purple. While the colors produced by the classical methods are typically permanent, the colors produced by organic dyes can fade with exposure to light or heat.^[41] Organic dyes can also only penetrate a short distance into the agate from the exposed surfaces. The practice of artificially treating agates remains popular today, and dyed Brazilian agates in particular are very common on the global market.^[1]Template:Rp

Larger agates are often cut into halves or slices with circular diamond saws. They can then be polished with lapidary grinding, sanding, and polishing wheels of successively greater grit sizes.^[1]Template:Rp Smaller agates and crushed agate fragments can alternatively be polished using rock tumblers or vibratory polishers. This equipment can generate large quantities of silica dust. Respiratory diseases such as silicosis, and a higher incidence of tuberculosis among workers involved in the agate industry, have been studied in India and China.^[42]^[43]^[44]

Notes

Template:Notelist

References

Template:Reflist

External links

Template:Sister project

"Agates", School of Natural Resources, University of Nebraska-Lincoln (retrieved 27 December 2014).

Template:Silica minerals Template:Gemstones Template:Jewellery Template:Authority control

↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa ^ab ^ac ^ad ^ae ^af ^ag ^ah ^ai ^aj ^ak ^al ^am ^an ^ao ^ap ^aq ^ar ^as ^at ^au ^av ^aw ^ax ^ay ^az ^ba ^bb ^bc ^bd ^be ^bf ^bg Script error: No such module "citation/CS1".
↑ ^a ^b ^c ^d ^e ^f ^g ^h Script error: No such module "citation/CS1".
↑ ^a ^b ^c Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "citation/CS1".
↑ ^a ^b ^c ^d ^e ^f Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ ^a ^b Script error: No such module "citation/CS1".
↑ ^a ^b Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ ^a ^b Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ ^a ^b Script error: No such module "citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ Script error: No such module "citation/CS1".
↑ C. Michael Hogan. 2007. Knossos fieldnotes, Modern Antiquarian Template:Webarchive
↑ Template:Cite magazine
↑ Script error: No such module "citation/CS1".
↑ ^a ^b ^c ^d ^e ^f ^g ^h Script error: No such module "citation/CS1".
↑ ^a ^b ^c ^d Script error: No such module "citation/CS1".
↑ ^a ^b Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".
↑ Script error: No such module "Citation/CS1".

[pabian-1] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa ^ab ^ac ^ad ^ae ^af ^ag ^ah ^ai ^aj ^ak ^al ^am ^an ^ao ^ap ^aq ^ar ^as ^at ^au ^av ^aw ^ax ^ay ^az ^ba ^bb ^bc ^bd ^be ^bf ^bg Script error: No such module "citation/CS1".

[mindat-2] ↑ ^a ^b ^c ^d ^e ^f ^g ^h Script error: No such module "citation/CS1".

[chalcedony-3] Script error: No such module "citation/CS1".

[4] Script error: No such module "Citation/CS1".

[PSU-5] Script error: No such module "citation/CS1".

[lynch_formation-6] ↑ ^a ^b ^c ^d ^e ^f Script error: No such module "citation/CS1".

[moxon_2017-7] Script error: No such module "Citation/CS1".

[Moxon-8] Script error: No such module "Citation/CS1".

[9] Script error: No such module "Citation/CS1".

[10] Script error: No such module "citation/CS1".

[11] Script error: No such module "citation/CS1".

[12] Script error: No such module "citation/CS1".

[13] Script error: No such module "citation/CS1".

[14] Script error: No such module "citation/CS1".

[turritella-15] Script error: No such module "citation/CS1".

[lynch_water-level-16] Script error: No such module "citation/CS1".

[lynch_fortification-17] Script error: No such module "citation/CS1".

[lynch_brecciated-18] Script error: No such module "citation/CS1".

[19] Script error: No such module "citation/CS1".

[20] Script error: No such module "citation/CS1".

[lynch_eyes-21] Script error: No such module "citation/CS1".

[22] Script error: No such module "citation/CS1".

[lynch_tubes-23] Script error: No such module "citation/CS1".

[lynch_dendritic-24] Script error: No such module "citation/CS1".

[25] Script error: No such module "citation/CS1".

[26] Script error: No such module "citation/CS1".

[27] Script error: No such module "citation/CS1".

[Antarctica-28] Script error: No such module "citation/CS1".

[29] Script error: No such module "Citation/CS1".

[30] Script error: No such module "citation/CS1".

[31] Script error: No such module "citation/CS1".

[32] Script error: No such module "citation/CS1".

[33] Script error: No such module "citation/CS1".

[34] Script error: No such module "citation/CS1".

[lynch_whole_book-35] Script error: No such module "citation/CS1".

[36] C. Michael Hogan. 2007. Knossos fieldnotes, Modern Antiquarian Template:Webarchive

[37] Template:Cite magazine

[38] Script error: No such module "citation/CS1".

[russell-39] ↑ ^a ^b ^c ^d ^e ^f ^g ^h Script error: No such module "citation/CS1".

[treated_gem-40] Script error: No such module "citation/CS1".

[color_loss-41] Script error: No such module "Citation/CS1".

[42] Script error: No such module "Citation/CS1".

[43] Script error: No such module "Citation/CS1".

[44] Script error: No such module "Citation/CS1".

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

[34]

[35]

[36]

[37]

[38]

[39]

[40]

[41]

[42]

[43]

[44]

Agate: Difference between revisions

Latest revision as of 22:25, 19 November 2025

Contents

Etymology

Composition

Formation

Structural varieties

Wall-banded agates

Level-banded agates

Regional varieties

Uses

Treatment and processing

See also

Notes

References

External links

Navigation menu

@@ Line 1: / Line 1: @@
-{{short description|Banded variety of chalcedony}}
+{{Short description|Banded variety of chalcedony}}
-{{other uses}}
+{{Other uses}}
+{{Good article}}
 {{Infobox mineral
 | name = Agate
@@ Line 7: / Line 8: @@
 | boxbgcolor =#bb361c
 | boxtextcolor = #fff
-| image = Mexican Crazy Lace Agate - World's Best.jpg
+| image = Malawi Agate (Malawi, southeastern Africa) (32734668126).jpg
 | imagesize = 260px
-| caption = {{cvt|19.6|kg|lb|0}} specimen of crazy lace agate from Chihuahua, Mexico next to a tennis ball; {{cvt|38.2|cm|in}} wide
+| caption = Polished agate nodule from Malawi, Africa
 | formula = SiO<sub>2</sub> ([[silicon dioxide]])
 | molweight =
@@ Line 27: / Line 28: @@
 | streak = White
 | gravity = 2.60–2.64
-| density = 2.6 g/cm³
+| density = 2.6 g/cm<sup>3</sup>
 | melt =
 | tenacity = Brittle
@@ Line 35: / Line 36: @@
 | diaphaneity = Transparent to opaque (usually translucent)
 | other =
-| references= <ref name="mindat" /><ref>{{cite web |title=Agate |url=https://www.gemdat.org/gem-51.html |website=gemdat.org |access-date=9 March 2025}}</ref><ref>{{cite web |title=Agate Value, Price, and Jewelry Information |url=https://www.gemsociety.org/article/agate-gem-information/ |website=gemsociety,org |publisher=International Gem Society |access-date=9 March 2025}}</ref>
+| references= <ref name="mindat" /><ref>{{cite web |title=Agate |url=https://www.gemdat.org/gem-51.html |website=gemdat.org |access-date=9 March 2025}}</ref><ref>{{cite web |title=Agate Value, Price, and Jewelry Information |url=https://www.gemsociety.org/article/agate-gem-information/ |website=gemsociety.org |publisher=International Gem Society |access-date=9 March 2025}}</ref>
 }}
-'''Agate''' ({{IPAc-en|ˈ|æ|ɡ|ɪ|t}} {{respell|AG|it}}) is a banded variety of [[chalcedony]]. Agate stones are characterized by alternating bands of different colored chalcedony and sometimes include [[Macroscopic scale|macroscopic]] quartz. They are common in nature and can be found globally in a large number of different varieties. There are some varieties of chalcedony without bands that are commonly called agate ([[moss agate]], [[fire agate]], etc.); however, these are more properly classified solely as varieties of chalcedony. Agates are primarily formed as nodules within [[volcanic rock]], but they can also form in [[Vein (geology)|veins]] or in [[sedimentary rock]]. Agate has been popular as a [[gemstone]] in [[Jewellery|jewelry]] for thousands of years, and today it is also popular as a collector's stone. Some duller agates sold commercially are artificially dyed to enhance their color.
+'''Agate''' ({{IPAc-en|ˈ|æ|ɡ|ɪ|t}} {{respell|AG|it}}) is a variously translucent, banded variety of [[chalcedony]]. Agate stones are characterized by alternating bands of different colored chalcedony and may also include visible [[quartz]] crystals. They are common in nature and can be found globally in a large number of different varieties. There are some varieties of chalcedony without bands that are commonly called agate ([[moss agate]], [[fire agate]], etc.); however, these are not true agates. Moreover, not every banded chalcedony is an agate; for example, banded [[chert]] forms via different processes and is opaque. Agates primarily form as nodules within [[volcanic rock]], but they can also form in [[Vein (geology)|veins]] or [[Silicification|silicified]] fossils. Agate has been popular as a [[gemstone]] in [[Jewellery|jewelry]] for thousands of years, and today it is also popular as a collector's stone. Some duller agates sold commercially are artificially treated to enhance their color.
 ==Etymology ==
-Agate was given its name by [[Theophrastus]], a [[Greeks|Greek]] [[philosopher]] and [[naturalist]]. He discovered the stone c. 350 BCE along the shoreline of the River Achates ({{langx|grc|Ἀχάτης}}), now the [[Dirillo|Dirillo River]], on the [[Italy|Italian]] island of [[Sicily]], which at the time was a Greek territory.<ref name="pabian" />{{rp|pp=52,162}}
+Agate was given its name by [[Theophrastus]], a [[Greeks|Greek]] [[philosopher]] and [[naturalist]]. He discovered the stone {{circa|350 BCE}} along the shoreline of the River Achates ({{langx|grc|Ἀχάτης}}), now the [[Dirillo|Dirillo River]], on the [[Italy|Italian]] island of [[Sicily]], which at the time was a Greek territory.<ref name="pabian" />{{rp|pp=52,162}}
-==Formation and properties==
+==Composition==
-[[File:Agate- & quartz-lined geode 5 (32375570960).jpg|thumb|Geode agate]]
+Agate is composed principally of chalcedony,<ref name="mindat" /> a [[Microscopic scale|microscopic]] ([[microcrystalline]]) and submicroscopic ([[cryptocrystalline]]) form of quartz that grows in fibers. The chemical composition of quartz is {{chem2|SiO2}}, also known as [[silica]]. Normally, between 1% and 20% of the "quartz" in chalcedony is actually [[moganite]], a quartz [[Crystal polymorphism|polymorph]].<ref name="chalcedony" /> Unlike [[Macroscopic scale|macroscopic]] (macrocrystalline) quartz, which is [[anhydrous]], chalcedony normally contains very small amounts of water bound to its crystal structure.<ref name="chalcedony" /><ref name="pabian" />{{rp|p=11}}
-Agates are most commonly found as [[Nodule (geology)|nodules]] within the cavities of [[volcanic rock]]s<ref name="Moxon" /> such as [[basalt]], [[andesite]], and [[rhyolite]]. These cavities, called [[Vesicle (geology)|''vesicles'']] (''amygdaloids'' when filled),<ref name="pabian" />{{rp|p=12}} are gas bubbles that were trapped inside the lava when it cooled.<ref name="Moxon">{{Cite journal |last=Moxon |first=T |last2=Reed |first2=S. J. B. |year=2006 |title=Agate and chalcedony from igneous and sedimentary hosts aged from 13 to 3480 Ma: a cathodoluminescence study |url=https://pubs.geoscienceworld.org/gsa/minmag/article/70/5/485/140307 |url-status=live |journal=Mineralogical Magazine |volume=70 |issue=5 |pages=485–498 |bibcode=2006MinM...70..485M |doi=10.1180/0026461067050347 |s2cid=54607138 |archive-url=https://web.archive.org/web/20220313041353/https://pubs.geoscienceworld.org/gsa/minmag/article/70/5/485/140307 |archive-date=March 13, 2022 |access-date=October 1, 2006|url-access=subscription }}</ref><ref name="lynch formation">{{Cite book |last=Lynch |first=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=11–13}}</ref><ref name="pabian" />{{rp|p=12}} The vesicles are later filled with hot, silica-rich water from the surrounding environment, forming a silica gel. This gel crystallizes through a complex process to form agates. Since agates usually form in lavas poor in free silica, there are multiple theories of where the silica originates from, including micro-shards of silica glass from [[volcanic ash]] or [[tuff]] deposits and decomposing plant or animal matter.<ref name="pabian" />{{rp|p=11}} Agates are much harder than the rocks they form in, so they are frequently found detached from their host rock.
+Agate contains multiple layers, or bands, of chalcedony fibers.<ref name="mindat" /> The fibers are twisted,<ref>{{cite journal |last1=Wang|first1=Yifeng |last2=Merino|first2=Enrique |date=1990-06-01 |title=Self-organizational origin of agates: Banding, fiber twisting, composition, and dynamic crystallization model |journal=[[Geochimica et Cosmochimica Acta]] |language=en |volume=54 |issue=6 |pages=1627–1638 |doi=10.1016/0016-7037(90)90396-3 |bibcode=1990GeCoA..54.1627W |issn=0016-7037}}</ref><ref name="pabian" />{{rp|p=11}} forming a [[helix|helical]] shape.<ref name="PSU" /> There are two different types of chalcedony fibers: length-slow (also known as ''quartzine'') and length-fast. Agate primarily contains length-fast chalcedony fibers, consisting of crystals stacked perpendicular to the c-axis (side to side). Some intergrown quartzine may also be present, consisting of quartz crystals stacked parallel to the c-axis (tip to tip).<ref name="chalcedony">{{cite web |title=Chalcedony |url=https://www.mindat.org/min-960.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=18 September 2025}}</ref>
-Geologists generally understand the early stages of agate formation, but the specific processes that result in band development are still widely debated. Since they form in cavities within host rock, agate formation cannot be directly observed,<ref name="lynch formation" /> and unlike most other crystals, agates have never been successfully lab-grown.<ref>{{cite web |last1=Brown |first1=Nancy Marie |title=How Do Agates Form? |url=https://www.psu.edu/news/research/story/how-do-agates-form |website=psu.edu |publisher=The Pennsylvania State University |date=31 August 2001|access-date=3 March 2025}}</ref>
+Agate can sometimes contain small amounts of [[opal]], an [[amorphous]], hydrated form of silica.<ref name="pabian" />{{rp|p=11}} Agates also frequently contain macrocrystalline quartz, particularly in the center.<ref name="lynch formation" /><ref name="pabian" />{{rp|p=18}}
-Agate is composed of multiple bands, or layers, of chalcedony fibers,<ref>{{cite journal |last1=Wang|first1=Yifeng |last2=Merino|first2=Enrique |date=1990-06-01 |title=Self-organizational origin of agates: Banding, fiber twisting, composition, and dynamic crystallization model |journal=[[Geochimica et Cosmochimica Acta]] |language=en |volume=54 |issue=6 |pages=1627–1638 |doi=10.1016/0016-7037(90)90396-3 |bibcode=1990GeCoA..54.1627W |issn=0016-7037}}</ref> specifically length-fast chalcedony fibers and sometimes quartzine (length-slow chalcedony fibers).<ref name="mindat" /> Agate can also contain [[opal]], an [[amorphous]], hydrated form of silica.<ref name="pabian" />{{rp|p=11}} In ''wall-banded agates'', the fibers grow radially from the vesicle walls inward, perpendicular to the direction of the bands.<ref name="mindat">{{Cite web |title=Agate |url=https://www.mindat.org/min-51.html |access-date=10 February 2025 |website=mindat.org |publisher=Hudson Institute of Mineralogy}}</ref><ref>{{Cite web|url=https://www.ingentaconnect.com/content/schweiz/njma/2009/00000186/00000002/art00001|title=The formation of agate structures: models for silica transport, agate layer accretion, and for flow patterns and flow regimes in infiltration channels|last1=Walger|first1=Eckart|last2=Mattheß|first2=Georg|date=August 2009|website=www.ingentaconnect.com|language=en|access-date=March 3, 2020|last3=von Seckendorff|first3=Volker|last4=Liebau|first4=Friedrich|archive-date=June 4, 2018|archive-url=https://web.archive.org/web/20180604062121/https://www.ingentaconnect.com/content/schweiz/njma/2009/00000186/00000002/art00001|url-status=live}}</ref> The vesicle walls are often coated with thin layers of [[celadonite]] or [[chlorite]],<ref name="lynch formation"/><ref name="pabian" />{{rp|p=18}} soft, green [[phyllosilicate]] minerals that form from the reaction of hot, silica-rich water with the rock.<ref name="lynch formation" /> This coating provides a rough surface for the chalcedony fibers to form on, initially as radial [[spherulites]]. The rough surface also causes agate husks to have a pitted appearance once the coating has been weathered away or removed.<ref name="pabian" />{{rp|pp=18–19}} Sometimes, the spherulites grow around mineral inclusions, resulting in eyes, tubes, and sagenitic agates. The first layer of spherulitic chalcedony is typically clear, followed by successive growth bands of chalcedony alternated with chemically precipitated color bands, primarily [[iron oxides]].<ref name="pabian" />{{rp|p=13}} The center is often macrocrystalline quartz (quartz with visible crystals),<ref name="lynch formation" /> which can also occur in bands and forms when there is not enough water in the silica gel to promote chalcedony [[polymerization]].<ref name="pabian" />{{rp|p=18}} When the silica concentration of the gel is too low, a hollow center forms, called an agate ''geode''.<ref name=":02">{{Cite web|url=http://www.minerals.net/MineralDefinition.aspx?name=agate|title=Agate chalcedony: The mineral Agate information and pictures|website=www.minerals.net|language=en-US|access-date=2020-02-27|archive-date=2020-03-16|archive-url=https://web.archive.org/web/20200316005135/https://www.minerals.net/MineralDefinition.aspx?name=agate|url-status=live}}</ref><ref name="pabian" />{{rp|p=17}}
+==Formation==
-Quartz forms crystals around the cavity, with the apex of each crystal pointing towards the center. Occasionally, the quartz may be colored, such as [[amethyst]] or [[smoky quartz]]. ''Level-banded agates'' form when chalcedony precipitates out of solution in the direction of gravity, resulting in horizontal layers of microscopic chalcedony spherulites.<ref name="mindat" /> [[Enhydro agate|''Enhydro agates'']], or ''enhydros'', form when water becomes trapped within an agate (or chalcedony) nodule or geode, often long after its formation.<ref>{{cite book |last1=Bates |first1=R. L. |last2=Jackson |first2=J. A. |title=Glossary of Geological Terms |date=1987 |publisher=American Geological Institute |location=Alexandria, Virginia |page=788 |edition=3rd |url=https://www.gamineral.org/writings/enhydros-gray.html |access-date=9 March 2025}}</ref><ref>{{cite web |title=Enhydro Agate |url=https://www.mindat.org/min-7596.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=9 March 2025}}</ref>
+[[File:Agate- & quartz-lined geode 5 (32375570960).jpg|thumb|Agate geode]]
-Agates can also form within rock fissures, called ''veins''.<ref name="pabian" />{{rp|pp=11–12}} Vein agates form in a manner similar to nodular agates, and they include most lace agates, such as blue lace agate and crazy lace agate.
+Geologists generally understand the early stages of agate formation, but the specific processes that result in band development are widely debated. Since they form in cavities within host rock, agate formation cannot be directly observed,<ref name="lynch formation" /> and agate banding has never been successfully replicated in the lab.<ref name="PSU">{{cite web |last1=Brown |first1=Nancy Marie |title=How Do Agates Form? |url=https://www.psu.edu/news/research/story/how-do-agates-form |website=psu.edu |publisher=The Pennsylvania State University |date=31 August 2001|access-date=3 March 2025}}</ref><ref name="moxon 2017">{{cite journal |last1=Moxon |first1=Terry |title=A re-examination of water in agate and its bearing on the agate genesis enigma |journal=Mineralogical Magazine |date=October 2017 |volume=81 |issue=5 |pages=1223–1244 |doi=10.1180/minmag.2017.081.002 |url=https://www.cambridge.org/core/journals/mineralogical-magazine/article/abs/reexamination-of-water-in-agate-and-its-bearing-on-the-agate-genesis-enigma/81967BDA3CFFBCE5CD23385B8BF47752 |url-access=subscription |access-date=16 October 2025}}</ref>
-Less commonly, agates can form as nodules within [[sedimentary rock]], such as [[limestone]], [[Dolomite (rock)|dolomite]] or [[tuff]]. These agates form when silica replaces another mineral, or silica-rich water fills cavities left by decomposed plant or animal matter.<ref name="pabian" />{{rp|p=11–12}} Sedimentary agates also include ''fossil agates'', which form when silica replaces the original composition of an organic material.<ref>{{cite web |title=Fossil Agate |url=https://www.mindat.org/min-7603.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=9 March 2025}}</ref> This process is called [[silicification]], a form of [[petrification]]. Examples include [[petrified wood]],<ref>{{cite web |title=Petrified Wood |url=https://www.mindat.org/min-8018.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=9 March 2025}}</ref> agatized coral,<ref>{{cite web |title=Agatized coral |url=https://www.mindat.org/min-43510.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=9 March 2025}}</ref> and Turritella agate ([[Elimia tenera]]).<ref name="turritella" /> Although these fossils are often referred to as being "agatized", they are only true agates when they are banded.<ref name="mindat" />
+{{anchor|Nodular agate}}Agates are most commonly found as [[Nodule (geology)|nodules]] within the cavities of volcanic rocks<ref name="Moxon" /> such as [[basalt]], [[andesite]], and [[rhyolite]]. These cavities, called [[Vesicle (geology)|''vesicles'']] (''amygdaloids'' when filled),<ref name="pabian" />{{rp|p=12}} are gas bubbles that were trapped inside the lava when it cooled.<ref name="Moxon">{{Cite journal |last1=Moxon |first1=T |last2=Reed |first2=S. J. B. |year=2006 |title=Agate and chalcedony from igneous and sedimentary hosts aged from 13 to 3480 Ma: a cathodoluminescence study |url=https://pubs.geoscienceworld.org/gsa/minmag/article/70/5/485/140307 |url-status=live |journal=Mineralogical Magazine |volume=70 |issue=5 |pages=485–498 |bibcode=2006MinM...70..485M |doi=10.1180/0026461067050347 |s2cid=54607138 |archive-url=https://web.archive.org/web/20220313041353/https://pubs.geoscienceworld.org/gsa/minmag/article/70/5/485/140307 |archive-date=March 13, 2022 |access-date=October 1, 2006|url-access=subscription }}</ref><ref name="lynch formation">{{Cite book |last1=Lynch |first1=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=11–13}}</ref><ref name="pabian" />{{rp|p=12}} The vesicles are later filled with hot, silica-rich water from the surrounding environment, forming a silica gel. This gel crystallizes through a complex process to form agates.<ref name="pabian" />{{rp|pp=12-15}} Since agates usually form in lavas poor in free silica, there are multiple theories of where the silica originates from, including micro-shards of silica glass from [[volcanic ash]] or [[tuff]] deposits and decomposing plant or animal matter.<ref name="pabian" />{{rp|p=11}} Agates are much harder than the rocks they form in; some varieties (e.g. [[Lake Superior agate]]s) are frequently found detached from their host rock.<ref name="pabian" />{{rp|p=84}}
-==Varieties (by structure)==
+{{anchor|Wall-banded agate}}In ''wall-banded agates'', chalcedony fibers grow radially from the vesicle walls inward, perpendicular to the direction of the bands.<ref name="mindat">{{Cite web |title=Agate |url=https://www.mindat.org/min-51.html |access-date=10 February 2025 |website=mindat.org |publisher=Hudson Institute of Mineralogy}}</ref><ref>{{Cite journal|url=https://www.ingentaconnect.com/content/schweiz/njma/2009/00000186/00000002/art00001|title=The formation of agate structures: models for silica transport, agate layer accretion, and for flow patterns and flow regimes in infiltration channels|last1=Walger|first1=Eckart|last2=Mattheß|first2=Georg|date=August 2009|journal=Neues Jahrbuch für Mineralogie - Abhandlungen|language=en|access-date=March 3, 2020|last3=von Seckendorff|first3=Volker|last4=Liebau|first4=Friedrich|volume=186 |issue=2 |pages=113–152 |doi=10.1127/0077-7757/2009/0141 |bibcode=2009NJMA..186..113W |archive-date=June 4, 2018|archive-url=https://web.archive.org/web/20180604062121/https://www.ingentaconnect.com/content/schweiz/njma/2009/00000186/00000002/art00001|url-status=live}}</ref> The vesicle walls are often coated with thin layers of [[celadonite]] or [[chlorite]],<ref name="lynch formation"/><ref name="pabian" />{{rp|p=18}} soft, green [[phyllosilicate]] minerals that form from the reaction of hot, silica-rich water with the rock.<ref name="lynch formation" /> This coating provides a rough surface for the chalcedony fibers to form on, initially as radial [[spherulites]]. The rough surface also causes agate husks to have a pitted appearance once the coating has been weathered away or removed.<ref name="pabian" />{{rp|pp=18–19}} Sometimes, the spherulites grow around mineral inclusions, resulting in eyes, tubes, and sagenitic agates.<ref name="mindat" />
-Agates are broadly separated into two categories based the type of banding they exhibit.<ref name="lynch water-level" /><ref name="pabian" />{{rp|pp=24,36}} ''Wall banding'', also called ''concentric banding'' or ''adhesional banding'', occurs when agate bands follow the shape of the cavity they formed in. ''Level banding'', also called ''water-level banding,'' ''gravitational banding'', ''horizontal banding'', ''parallel banding'', or ''Uruguay-type banding'', occurs when agate bands form in straight, parallel lines. Level banding is less common and usually occurs together with wall banding.<ref name="mindat" />
+The first layer of spherulitic chalcedony is typically clear, followed by successive growth bands of chalcedony alternated with chemically precipitated color bands, primarily [[iron oxides]].<ref name="pabian" />{{rp|p=13}} The center is often macrocrystalline quartz,<ref name="lynch formation" /> which can also occur in bands and possibly forms when there is not enough chemically bound water in the silica gel to promote chalcedony [[polymerization]].<ref name="pabian" />{{rp|p=18}} When the silica concentration of the gel is too low, a hollow center forms, called an agate ''geode''. In geodes, quartz forms crystals around the cavity, with the apex of each crystal pointing towards the center. Occasionally, quartz in agates may be colored, occurring in [[Mineral variety|varieties]] such as [[amethyst]] or [[smoky quartz]].<ref name="pabian" />{{rp|p=17}}
+{{anchor|Level-banded agate}}''Level-banded agates'' form when chalcedony precipitates out of solution in the direction of gravity, resulting in horizontal layers of microscopic chalcedony spherulites.<ref name="mindat" /> Level banding commonly occurs together with wall banding, often forming at the base of the vesicle or in the center when the gel stops adhering to the vesicle walls. This is probably due to a decrease in bound water in the gel. Level-banded agate is less dense and less compact than wall-banded agate, as it is less fibrous and more granular.<ref name="pabian" />{{rp|p=19}}
+[[Enhydro agate|''Enhydro agates'']], or ''enhydros'', form when liquid water becomes trapped within an agate (or chalcedony) nodule or geode, often long after its formation.<ref>{{cite book |last1=Bates |first1=R. L. |last2=Jackson |first2=J. A. |title=Glossary of Geological Terms |date=1987 |publisher=American Geological Institute |location=Alexandria, Virginia |page=788 |edition=3rd |url=https://www.gamineral.org/writings/enhydros-gray.html |access-date=9 March 2025}}</ref><ref>{{cite web |title=Enhydro Agate |url=https://www.mindat.org/min-7596.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=9 March 2025}}</ref>
+{{anchor|Vein agate}}Agates can also form within rock fissures, called ''veins''.<ref name="pabian" />{{rp|pp=11–12}} Vein agates form in a manner similar to nodular agates (see above),<ref name="pabian" />{{rp|p=13}} and they include lace agates such as [[blue lace agate]] and crazy lace agate. Veins may form in either volcanic rock or [[Sedimentary rock|sedimentary]] rock.<ref name="pabian" />{{rp|p=50}}
+Less commonly, agates can form as nodules within sedimentary rocks such as [[limestone]], [[Dolomite (rock)|dolomite]] or tuff. These agates form when silica replaces another mineral, or silica-rich water fills cavities left by decomposed plant or animal matter.<ref name="pabian" />{{rp|p=11–12}} {{anchor|Fossil agate}}Sedimentary agates also include ''fossil agates'', which form when silica replaces the original composition of an organic material.<ref>{{cite web |title=Fossil Agate |url=https://www.mindat.org/min-7603.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=9 March 2025}}</ref> This process is called [[silicification]], a form of [[petrification]]. Examples include [[petrified wood]],<ref>{{cite web |title=Petrified Wood |url=https://www.mindat.org/min-8018.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=9 March 2025}}</ref> agatized coral,<ref>{{cite web |title=Agatized coral |url=https://www.mindat.org/min-43510.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=9 March 2025}}</ref> and Turritella agate ([[Elimia tenera]]).<ref name="turritella" /> Although these fossils are often referred to as being "agatized", they are only true agates if they contain bands.<ref name="mindat" />
+==Structural varieties==
+Agates are broadly separated into two categories based on the type of banding they exhibit.<ref name="lynch water-level" /><ref name="pabian" />{{rp|pp=24,36}} ''[[#Wall-banded agate|Wall banding]]'', also called ''concentric banding'' or ''adhesional banding'', occurs when agate bands follow the shape of the cavity they formed in. ''[[#Level-banded agate|Level banding]]'', also called ''water-level banding,'' ''gravitational banding'', ''horizontal banding'', ''parallel banding'', or ''Uruguay-type banding'', occurs when agate bands form in straight, parallel lines. Level banding is less common and usually occurs together with wall banding.<ref name="mindat" />
+[[File:Agate 6 (32375570980).jpg|thumb|center|200px|Agate exhibiting wall banding (top) and level banding (bottom)]]
 === Wall-banded agates ===
-''Fortification agates'' have very tight, well-defined bands. They get their name from their appearance resembling the walls of a [[Fortification|fort]]. Fortification agates are one the most common varieties, and they are what most people think of when they hear the word "agate".<ref name="lynch fortification">{{Cite book |last=Lynch |first=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=22–25}}</ref>
+{{anchor|Fortification agate}}''Fortification agates'' are any wall-banded agates with tight, well-defined bands.<ref name="pabian" />{{rp|p=29}} They get their name from their appearance which resembles the walls of a [[Fortification|fort]]. Fortification agates are one the most common varieties, and they are what most people think of when they hear the word "agate".<ref name="lynch fortification">{{Cite book |last1=Lynch |first1=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=22–25}}</ref>
-''Lace agates'' exhibit a [[lace]]-like pattern of bands with many swirls, eyes, bends, and zigzags. Unlike most agates, they usually form in [[Vein (geology)|veins]] instead of [[Nodule (geology)|nodules]].<ref name="pabian" />{{rp|p=31}}
-''Faulted agates'' occur when agate bands are broken and slightly shifted by rock movement and then re-cemented together by chalcedony. They have the appearance of rock layers with [[Fault (geology)|fault lines]] running through them. ''Brecciated agates'' have also had their bands broken apart and re-cemented with chalcedony, but they consist of disjointed band fragments at random angles.<ref name="lynch brecciated">{{Cite book |last=Lynch |first=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=70–73}}</ref><ref name="pabian" />{{rp|pp=24,28}} They are a form of [[breccia]], which is a textural term for any rock composed of angular fragments.<ref name="lynch brecciated" /><ref>{{Cite web |title=Brecciated agate |url=https://www.mindat.org/min-7593.html |access-date=February 11, 2025 |website=Mindat.org |publisher=Hudson Institute of Mineralogy}}</ref>
+{{anchor|Lace agate}}''Lace agates'' exhibit a [[lace]]-like pattern of bands with many swirls, eyes, bends, and zigzags. Unlike most agates, they usually form in veins instead of nodules.<ref name="pabian" />{{rp|p=31}}
-''Eye agates'' have one or more circular, concentric rings on their surface.<ref>{{Cite web |title=Eye Agate |url=https://www.mindat.org/min-7598.html |access-date=February 11, 2025 |website=Mindat.org |publisher=Hudson Institute of Minerology}}</ref> These "eyes" are actually [[Hemisphere (geometry)|hemispheres]] that form on the husk of the agate and extend inward like a bowl.<ref name="lynch eyes">{{Cite book |last=Lynch |first=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=82–85}}</ref> ''Tube agates'' contain tunnel-like structures that extend all the way through the agate.<ref name="lynch tubes">{{Cite book |last=Lynch |first=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=64–67}}</ref> These "tubes" may sometimes be banded or hollow, or both. Both tube and eye agates form when chalcedony grows around a needle-shaped crystal of another mineral embedded within the agate, forming [[Stalactite|stalactitic]] structures. Visible "eyes" can also appear on the surface of tube agates if a cut is made (or the agate is weathered) perpendicular to the stalactitic structure.<ref name="pabian" />{{rp|pp=27,35}}
+{{anchor|Faulted agate}}''Faulted agates'' have bands that were broken and slightly shifted by rock movement and then re-cemented together by chalcedony. They have the appearance of rock layers with [[Fault (geology)|fault lines]] running through them. ''Brecciated agates'' also have bands that were broken apart and re-cemented with chalcedony, but they consist of disjointed band fragments at random angles.<ref name="lynch brecciated">{{Cite book |last1=Lynch |first1=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=70–73}}</ref><ref name="pabian" />{{rp|pp=24,28}} They are a form of [[breccia]], which is a textural term for any rock composed of angular fragments.<ref name="lynch brecciated" /><ref>{{Cite web |title=Brecciated agate |url=https://www.mindat.org/min-7593.html |access-date=February 11, 2025 |website=Mindat.org |publisher=Hudson Institute of Mineralogy}}</ref>
-''Dendritic agates'' have dark-colored, fern-like patterns ([[Dendrite (crystal)|dendrites]]) on the surface or the spaces between bands.<ref name="lynch dendritic">{{Cite book |last=Lynch |first=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=78–81}}</ref><ref name="pabian" />{{rp|p=25}} They are composed of manganese or iron oxides. ''[[Moss agate]]s'' exhibit a [[moss]]-like pattern and are usually green or brown in color. They form when dendritic structures on the surface of an agate are pushed inward with the silica gel during their formation. Moss agate was once believed to be petrified moss, until it was discovered the moss-like formations are actually composed of [[celadonite]], [[hornblende]], or a [[Chlorite group|chlorite]] mineral. ''Plume agates'' are a type of moss agate, but the dendritic "plumes" form tree-like structures within the agate. They are often bright red (from inclusions of [[hematite]]) or bright yellow (from inclusions of [[goethite]]).<ref name="pabian" />{{rp|pp=32–33}} While dendrites frequently occur in banded agates, moss and plume agates usually lack bands altogether. Therefore, they are not true agates according to the mineralogical definition.<ref name="mindat" /><ref>{{Cite web |last=Team |first=Geology In |title=Moss Agate: Formation, Occurrence, Uses |url=https://www.geologyin.com/2020/02/what-is-moss-agate.html#google_vignette |access-date=2025-02-11 |website=Geology In |language=en}}</ref>
+{{anchor|Eye agate}}''Eye agates'' have one or more circular, concentric rings on their surface.<ref>{{Cite web |title=Eye Agate |url=https://www.mindat.org/min-7598.html |access-date=February 11, 2025 |website=Mindat.org |publisher=Hudson Institute of Mineralogy}}</ref> These "eyes" are actually [[Hemisphere (geometry)|hemispheres]] that form on the husk of the agate and extend inward like a bowl.<ref name="lynch eyes">{{Cite book |last1=Lynch |first1=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=82–85}}</ref>
-''Iris agates'' have bands that are so microscopically fine that when thinly sliced, they cause white light to be [[Diffraction|diffracted]] into its [[spectrum|spectral]] colors. This "iris effect" usually occurs in colorless agates, but it can also occur in brightly colored ones.<ref name="pabian" />{{rp|p=30}}
+{{anchor|Sagenitic agate}}''Sagenitic agates'', or ''sagenites'', have [[Acicular (crystal habit)|acicular]] (needle-shaped) inclusions of another mineral, usually [[anhydrite]], [[aragonite]], goethite, [[rutile]], or a [[zeolite]]. Chalcedony often forms tubes around these crystals and may eventually replace the original mineral, resulting in a [[pseudomorph]].<ref name="pabian" />{{rp|p=34}} The term "sagenite" was originally a name for a type of rutile, and later [[rutilated quartz]]. It has since been used to describe any quartz variety with acicular inclusions of any mineral.<ref>{{cite web |title=Sagenite |url=https://www.mindat.org/min-8578.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=16 February 2025}}</ref>
-''Sagenitic agates'', or ''sagenites'', have [[Acicular (crystal habit)|acicular]] (needle-shaped) inclusions of another mineral, usually [[anhydrite]], [[aragonite]], [[goethite]], [[rutile]], or a [[zeolite]]. Chalcedony often forms tubes around these crystals and may eventually replace the original mineral, resulting in a [[pseudomorph]].<ref name="pabian" />{{rp|p=34}} The term "sagenite" was originally a name for a type of rutile, and later [[rutilated quartz]]. It has since been used to describe any quartz variety with acicular inclusions of any mineral.<ref>{{cite web |title=Sagenite |url=https://www.mindat.org/min-8578.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=16 February 2025}}</ref>
+{{anchor|Tube agate}}''Tube agates'' contain tunnel-like structures that extend all the way through the agate.<ref name="lynch tubes">{{Cite book |last1=Lynch |first1=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=64–67}}</ref> These "tubes" may sometimes be banded or hollow, or both. Tube agates form when chalcedony grew around sagenitic inclusions embedded within the agate, forming [[Stalactite|stalactitic]] structures. Visible "eyes" can also appear on the surface of tube agates if a cut is made (or the agate is weathered) perpendicular to the stalactitic structure.<ref name="pabian" />{{rp|pp=27,35}}
-=== Level-banded agates ===
+{{anchor|Dendritic agate}}''Dendritic agates'' have dark-colored, fern-like patterns ([[Dendrite (crystal)|dendrites]]) that form on the surface or in the spaces between bands.<ref name="lynch dendritic">{{Cite book |last1=Lynch |first1=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=78–81}}</ref><ref name="pabian" />{{rp|p=25}} They are composed of manganese or iron oxides. ''Moss agates'' exhibit a [[moss]]-like pattern and are usually green or brown in color. They form when dendritic structures on the surface of an agate are pushed inward with the silica gel during their formation. Moss agate was once believed to be petrified moss, until it was discovered the moss-like formations are actually composed of celadonite, [[hornblende]], or a [[Chlorite group|chlorite]] mineral. ''Plume agates'' are a type of moss agate, but the dendritic "plumes" form tree-like structures within the agate. They are often bright red (from inclusions of [[hematite]]) or bright yellow (from inclusions of [[goethite]]).<ref name="pabian" />{{rp|pp=32–33}} While dendrites frequently occur in banded agates, moss and plume agates usually lack bands altogether. Therefore, they are not true agates according to the mineralogical definition.<ref name="mindat" /><ref>{{Cite web |last=Team |first=Geology In |title=Moss Agate: Formation, Occurrence, Uses |url=https://www.geologyin.com/2020/02/what-is-moss-agate.html#google_vignette |access-date=2025-02-11 |website=Geology In |language=en}}</ref>
-Agates with level banding are traditionally called ''[[onyx]]'', although the formal definition of the term onyx refers to color pattern, not the shape of the bands.<ref>{{cite web |title=Onyx |url=https://www.mindat.org/min-2999.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=February 9, 2025}}</ref> Accordingly, the name "onyx" is also used for wall-banded agates. Onyx is also frequently misused as a name for banded [[calcite]]. The name originates from the Greek word for the human nail, which has parallel ridges.<ref name="pabian">{{Cite book |last=Pabian |first=Roger |title=Agates: Treasures of the Earth |last2=Jackson |first2=Brian |last3=Tandy |first3=Peter |last4=Cromartie |first4=John |date=2016 |publisher=Firefly Books |isbn=978-1-77085-644-8}}</ref>{{rp|p=37}} Typically, onyx bands alternate between black and white or other light and dark colors. ''Sardonyx'' is a variety with red-to-brown bands alternated with either white or black bands.<ref>{{cite web |title=Sardonyx |url=https://www.mindat.org/min-7604.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date= February 10, 2025}}</ref>
-[[Thunderegg|Thunder eggs]] are frequently level-banded, however they may also have wall banding. Level banding is also common in [[Lake Superior agate]]s.<ref name="lynch water-level">{{Cite book |last=Lynch |first=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=34–37}}</ref>
+{{anchor|Iris agate}}''Iris agates'' have bands that are fine enough that when thinly sliced, they cause white light to be [[Diffraction|diffracted]] into its [[spectrum|spectral]] colors. This "iris effect" usually occurs in colorless agates, but it can also occur in brightly colored ones.<ref name="pabian" />{{rp|p=30}}
 <gallery mode="packed" heights="130px">
-Agate 6 (32375570980).jpg|Agate with both wall banding (top) and level banding (bottom)
 Agate Braziilia.jpg|Brazilian agate with classic fortification banding
-Crazy Lace Agate 06.jpg|Crazy lace agate
 Eyeballed by all the eye agates (27395607964).jpg|Tumbled Lake Superior eye agates
 Detail, Dendritic agate (cropped).jpg|Dendritic agate from India
 Four moss agate cabochons.jpg|Moss agate cabochons
 Iris Agate from (Agatized Petrified Wood), Stinking Water, Oregon detail, from- Oregon004 (cropped).jpg|Iris agate from petrified wood
-Agate D Bruyere.jpg|Level-banded agate
-Onyx Mainzer Becken.jpg|Onyx agate
-Thunder Egg Agate (Priday Blue Bed, John Day Formation, Miocene; near Madras, Oregon, USA) 5.jpg|Level-banded thunder egg from Oregon, USA
 </gallery>
-== Varieties (by locality) ==
+=== Level-banded agates ===
-Agates are very common, and they have been found on every continent, including Antarctica. In addition to names used to describe their structure, numerous geological, local, and trade names are applied to agates from different localities.<ref name="pabian" />{{rp|pp=7–9}} Below is a list of known agate localities and the names of the agates that are found there. This list is not exhaustive.
+Agates with level banding are traditionally called ''[[onyx]]'', although the formal definition of the term onyx refers to color pattern, not the shape of the bands.<ref>{{cite web |title=Onyx |url=https://www.mindat.org/min-2999.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=February 9, 2025}}</ref> Accordingly, the name ''onyx'' is also used for wall-banded agates. Onyx is also frequently misused as a name for banded [[calcite]]. The name originates from the Greek word for the human nail, which has parallel ridges.<ref name="pabian">{{Cite book |last1=Pabian |first1=Roger |title=Agates: Treasures of the Earth |last2=Jackson |first2=Brian |last3=Tandy |first3=Peter |last4=Cromartie |first4=John |date=2016 |publisher=Firefly Books |isbn=978-1-77085-644-8}}</ref>{{rp|p=37}} Typically, onyx bands alternate between black and white or other light and dark colors. ''Sardonyx'' is a variety with red-to-brown bands alternated with either white or black bands.<ref>{{cite web |title=Sardonyx |url=https://www.mindat.org/min-7604.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date= February 10, 2025}}</ref>
-=== Africa ===
+[[Thunderegg|Thunder eggs]] are frequently level-banded, however they may also have wall banding. Level banding is also common in [[Lake Superior agate]]s.<ref name="lynch water-level">{{Cite book |last1=Lynch |first1=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6 |pages=34–37}}</ref>
-* ''Blue lace agate'' is a pale blue and white lace agate found primarily in [[Namibia]]. These agates formed in dolomite associated with igneous rock.
-* ''Botswana agates'' are found in [[basalt]]ic rocks of the [[Permian]] age in [[Botswana]]. They feature contrasting bands of purple, pink, black, grey, and white. Like Lake Superior agates, they are typically small, averaging <!--CheckU-->{{convert|2.5|–|5|cm|in|abbr=on}} in diameter.
-* ''Malawi agates'' are typically bright red or orange with contrasting white bands, but some are pink and blue. They can be found in [[Malawi]], and they likely formed in volcanic rock of Permian age.
-* Agates have also been found in [[Egypt]], [[Madagascar]], [[South Africa]], and [[Zimbabwe]].<ref name="pabian" />{{rp|pp=131–137}}
-<gallery mode="packed" heights="130px">
-Blue Lace Agate from Namibia (polished).jpg|Blue lace agate
-Agat - Bobonong, Botswana.jpg|Botswana agate
-Malawi Agate (Malawi, southeastern Africa) (32734668126).jpg|Malawi agate
-</gallery>
-=== Antarctica ===
-* White and clear banded agates have been found by scientists at [[Bellingshausen Station]], a Russian outpost on [[King George Island (South Shetland Islands)|King George Island]].<ref>{{cite web |title=Collins Harbour, King George Island, South Shetland Islands, Antarctic Peninsula, Western Antarctica, Antarctica |url=https://www.mindat.org/loc-420174.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=16 February 2025}}</ref>
-[[File:Agate (Tertiary; Agate Bay, King George Island, South Shetland Islands) 1.jpg|thumb|center|215px|Agate from King George Island, Antarctica]]
-=== Asia ===
-* India has produced agates since as early as the 11th century. These include carnelian agates, moss agates, and dendritic agates.
-* Yemen is home to a variety of agate called ''mocha stone'', named after the port city of [[Mokha|Mocha]] (also spelled Mokha or Mukha) on the [[Red Sea]]. These agates likely formed in [[tuff]] deposits of [[Chattian|Late Oligocene]] and [[Early Miocene]] age.
-* Agates have also been found in [[Iran]], [[Mongolia]], [[China]],<ref name="pabian" />{{rp|pp=138–143}} and [[Russia]].<ref name="mindat" />
-[[File:Agates Mandalgobi (2).jpg|thumb|center|180px|Rough agates from the [[Gobi Desert]] in Mongolia]]
-=== Australia ===
-* ''Queensland agates,'' found in the State of [[Queensland]], often occur in colors that are rarely found in agates from other regions, such as green and yellow-green. They formed in basaltic lava flows of the Late Permian period. Level banding is common in Queensland agates, while inclusions are uncommon. Queensland is also home to several kinds of ''thunder egg'', which are thought to date from the [[Early Cretaceous]] period.
-* Agates have also been found in [[Tasmania]] and other regions of Australia.<ref name="pabian" />{{rp|pp=144–149}}
-[[File:Agat ze strefą krustalną - Agate Creek, Queensland, Australia.jpg|thumb|center|215px|Queensland agate with level banding]]
-=== Europe ===
-* Agate was discovered in [[Sicily]] by the Greek scholar Theophrastus in 350 BC. At the time, Sicily was a colony of [[ancient Greece]]. The name "agate" comes from the Achates River, the Greek name for what is now known as the [[Dirillo|Dirillo River]]. Agates in Sicily formed in balsaltic lavas and pyroclastic rocks of the [[Pliocene|Pilocene]] epoch.
-* [[Germany]] is a well-known historic source of agate. Agates mined from volcanic rock of the Permian period have been processed in [[Idar-Oberstein]] since at least 1375, but possibly as early as the [[Roman Empire]]. Agates from the Idar-Oberstein area are often red and pink, but other colors have also been observed. Many museum specimens include features such as eyes, tubes, moss, plumes, and sagenite.
-* [[Scotland]] is an abundant source of a wide variety of agates. There are at least 50 main agate localities in Scotland. Scottish agates have been popular in jewelry for several hundred years, particularly during the [[Victorian era]]. They formed in two types of rock: andesite from the [[Early Devonian]] period and basalt from the [[Tertiary]] period. The andesite deposits are more significant and extend from [[Stonehaven]] in the northeast to just south of [[Ayr]] in the southwest. The basaltic agates are confined to the islands off the west coast of Scotland and are collectively called the ''Small Isles agates''. The colors of Scottish agates vary, and bands may be different shades of blue, grey, purple, pink, brown, orange, or red.
-* ''Pot stones'' or ''potato stones'' are irregular agate nodules or geodes found in [[Bristol]] and [[Somerset]], England. They typically consist of a reddish, banded agate surrounding a hollow cavity lined with macroscopic quartz, although some are completely filled with agate. Other varieties of agate have also been found elsewhere in England.
-* Agates can also be found in [[Wales]], the [[Czech Republic]], [[Poland]], [[France]],<ref name="pabian" />{{rp|pp=52–75}} and many other European countries.<ref name="mindat" />
 <gallery mode="packed" heights="130px">
-Agate-MCG 91225-P4150832-white.jpg|German agate from Idar-Oberstein
+Onyx Mainzer Becken.jpg|Onyx agate
-Agate detail, Scotland 007 (cropped).jpg|Close-up of a Scottish agate from [[Ayrshire]]
+Thunder Egg Agate (Priday Blue Bed, John Day Formation, Miocene; near Madras, Oregon, USA) 5.jpg|Level-banded thunder egg from Oregon, USA
-Quartz-agate (12250382174).jpg|Potato stone from England
-Agate from Czech Republic (7).jpg|Agate from Czech Republic
 </gallery>
-=== North America ===
+== Regional varieties ==
-* ''Coldwater agates'', such as the [[Lake Michigan]] cloud agate, are sedimentary agates that formed within [[limestone]] and [[Dolomite (rock)|dolomite]] strata of marine origin. Like volcanic agates, Coldwater agates formed from silica gels that lined pockets and seams within the bedrock. These agates are typically less colorful, with banded lines of grey and white chalcedony.<ref>{{Cite book|last=Garvin|first=Paul|url=https://books.google.com/books?id=3a1XkpBGdAcC&q=Coldwater+agates&pg=PA65|title=Iowa's Minerals: Their Occurrence, Origins, Industries, and Lore|date=2010-09-13|publisher=University of Iowa Press|isbn=978-1-60938-014-4|language=en|access-date=2020-10-29|archive-date=2023-08-26|archive-url=https://web.archive.org/web/20230826164756/https://books.google.com/books?id=3a1XkpBGdAcC&q=Coldwater+agates&pg=PA65|url-status=live}}</ref>
+Agates are very common, and they have been found on every continent,<ref name="pabian" />{{rp|p=5}} including Antarctica.<ref name="Antarctica" /> In addition to the structural varieties detailed in the previous section, numerous geological, local, and trade names are used to describe agates from different localities.<ref name="pabian" />{{rp|pp=7–9}} Below is a table of agate varieties from different regions of the world.{{sticky header}}
-* ''Crazy lace agate'' is a brightly colored lace agate from [[Mexico]] with a complex pattern, demonstrating randomized distribution of contour lines and circular droplets, scattered throughout the rock. The stone is typically colored red and white but is also seen to exhibit yellow and grey combinations as well.<ref>{{Cite book|last1=Atkinson|first1=Bill|url=https://books.google.com/books?id=ZSP94tREw7AC&q=Crazy+lace+agate&pg=PA165|title=Within the Stone: Photography|last2=Ackerman|first2=Diane|date=2004|publisher=BrownTrout Publishers|isbn=978-0-7631-8189-5|language=en|access-date=2020-10-29|archive-date=2023-08-26|archive-url=https://web.archive.org/web/20230826164751/https://books.google.com/books?id=ZSP94tREw7AC&q=Crazy+lace+agate&pg=PA165|url-status=live}}</ref> Crazy lace agate is a vein agate that formed in sedimentary rock of the late [[Cretaceous]] period.<ref name="pabian" />{{rp|p=121}}
+{| class="wikitable sortable sticky-header" |
-* ''Dugway geodes'' are a type of thunder egg found in [[Utah]]. They are typically light grey to blue and often contain hollow cavities lined with drusy quartz.<ref name="pabian" />{{rp|p=92}}
+|+ Regional varieties of agate
-* [[Fairburn Agate|''Fairburn agates'']] are rare fortification agates named for [[Fairburn, South Dakota]]. They are sedimentary agates that originated during the [[Pennsylvanian (geology)|Pennsylvanian]] period, and then weathered from their host rock and redeposited during the [[Oligocene]] epoch in parts of South Dakota and [[Nebraska]].<ref>{{cite web |title=Fairburn Agate |url=https://www.mindat.org/min-1441.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=16 February 2025}}</ref>
+|-
-* ''Laguna agate'' is a brightly colored agate variety that was first discovered in Ojo Laguna, Chihuahua, Mexico.<ref>{{Cite web |title=Laguna Agate |url=https://www.mindat.org/min-7611.html |access-date=2025-02-16 |website=www.mindat.org}}</ref> It features vibrant bands in shades of red, orange, pink, or purple. Laguna agates formed in [[andesite]] and are geologically young. They frequently contain inclusions and many exhibit parallax or shadow banding.<ref name="pabian" />{{rp|pp=114–115}}
+! Name !! Locality !! Region !! Description !! Type !! Geologic environment !! Age !! Photo(s) !! References
-* ''[[Lake Superior agate]]s'' are believed to be the world's oldest agates;<ref>{{cite web |title=Lake Superior Agate |url=https://www.mindat.org/min-9253.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=16 February 2025}}</ref> they formed as nodules in basalt up to 1.2 billion years ago during the Late [[Precambrian]]. These agates are primarily found near the shores of [[Lake Superior]] in the [[United States|U.S.]] states of [[Minnesota]], [[Michigan]], and [[Wisconsin]], and in the [[Canada|Canadian]] province of [[Ontario]]. They are not named after the lake, but rather the Lake Superior [[Till]], the [[Pleistocene]] glacial deposit in which they are found.<ref name="pabian" />{{rp|pp=83–84}} This deposit also extends into portions of [[Iowa]], [[Nebraska]], [[Kansas]], and [[Missouri]], and Lake Superior agates have been carried south by the [[Mississippi River]] into [[Arkansas]] and [[Louisiana]]. Lake Superior agates have bands in shades of red, orange, yellow, brown, white, and grey. They can contain a variety of structural features, including eyes, tubes, sagenite, dendrites, faults, and geodes.<ref name="lynch whole book">{{Cite book |last=Lynch |first=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6}}</ref>
+|-
-* ''Lysite agate'' is a vein agate named after Lysite Mountain, [[Wyoming]]. It is frequently colorful and may contain moss and plumes in addition to bands.<ref name="pabian" />{{rp|p=79}}
+| [[Blue lace agate]] || Namibia || Africa || Pale blue and white lace agate || [[#Vein agate|Vein agate]] || Volcanic rock (dolomite associated with [[dolerite]])|| || [[File:Blue Lace Agate.jpg|thumb|center|Blue lace agate from Ysterputz Mine, Namibia]] || <ref name="pabian" />{{rp|pp=134-135}}
-* ''Nebraska blue agate'' is a sedimentary agate with dendritic patterns that formed during the Oligocene epoch. It can be found throughout northwestern Nebraska and southwestern South Dakota.<ref name="pabian" />{{rp|p=80}}
+|-
-* Oregon is known for several different varieties of agate. It is probably best known for its ''thunder eggs'', which form in rhyolitic ash and have a brown rhyolite shell that is usually filled with blue and white agate.<ref name="pabian" />{{rp|p=99}} ''Holley blue agate'' (also spelled "Holly blue agate") is a rare lavender to blue agate found only near [[Holley, Oregon]].<ref name="pabian" />{{rp|p=103}}
+| {{anchor|Botswana agate}}Botswana agate || Botswana || Africa || Typically {{convert|2.5|–|5|cm|in|abbr=on}} in diameter, with contrasting bands of purple, pink, black, grey, and white || [[#Nodular agate|Nodular agate]] || Volcanic rock (Karoo Series, basalt) || [[Permian]] period || [[File:Agat - Bobonong, Botswana.jpg|thumb|center|Botswana agate]] || <ref name="pabian" />{{rp|pp=131–132}}
-* ''[[Patuxent River stone]]'' is a red and yellow form of agate only found in [[Maryland]], where it is the state gem.<ref>{{cite web |title=Maryland State Gem - Patuxent River Stone |url=https://msa.maryland.gov/msa/mdmanual/01glance/symbols/html/gem.html |website=maryland.gov |publisher=Maryland State Archives |access-date=16 February 2025}}</ref>
+|-
-* ''Sweetwater agates'' are small moss agates found in [[Miocene]] age [[sandstone]] near Sweetwater River, Wyoming. They also contain brown or black dendrites and fluoresce under [[Ultraviolet|UV]] light.<ref name="pabian" />{{rp|p=79}}
+| {{anchor|Malawi agate}}Malawi agate || Malawi || Africa || Typically bright red or orange with contrasting white bands, some are pink and blue || [[#Nodular agate|Nodular agate]] || Volcanic rock || Permian period || || <ref name="pabian" />{{rp|p=134}}
-* ''Turritella agate'' is a brown fossil agate formed from the remains of an extinct species of freshwater snail ([[Elimia tenera]]) with an elongated spiral shell. The name is a misnomer; it was originally thought to be the fossil of a different genus of gastropods, [[Turritella]]. It is found in the [[Green River Formation]] of Wyoming.<ref name="turritella">{{Cite web |last=King |first=Hobart M. |title=Turritella Agate |url=https://geology.com/gemstones/turritella/ |access-date=16 February 2025 |website=geology.com}}</ref>
+|-
-* Other varieties of agate have also been found in nearly every U.S. state, northern Mexico, and in the Canadian provinces of [[Nova Scotia]], [[Manitoba]], and [[British Columbia]].<ref name="pabian" />{{rp|pp=76–121}}
+| (Unnamed agate) || [[Bellingshausen Station]], [[King George Island (South Shetland Islands)|King George Island]] || Antarctica || White and clear bands || [[#Nodular agate|Nodular agate]] || || || [[File:Agate (Tertiary; Agate Bay, King George Island, South Shetland Islands) 1.jpg|thumb|center|215px|Agate from King George Island, Antarctica]] || <ref name="Antarctica">{{cite web |title=Collins Harbour, King George Island, South Shetland Islands, Antarctic Peninsula, Western Antarctica, Antarctica |url=https://www.mindat.org/loc-420174.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=16 February 2025}}</ref>
-<gallery mode="packed" heights="130px">
+|-
-Crazy Lace Agate - Macro Panorama.jpg|Crazy lace agate
+| {{anchor|Queensland agate}}Queensland agate || [[Queensland]] || Australia || Often green or yellow-green (colors that are rarely found in other regions), frequently level-banded || [[#Nodular agate|Nodular agate]] || Volcanic rock (basaltic lava flows) || Late Permian period || [[File:Agat ze strefą krustalną - Agate Creek, Queensland, Australia.jpg|thumb|center|215px|Queensland agate with level banding]] || <ref name="pabian" />{{rp|pp=144–145}}
-Dugway Geode (Juab County, Utah, USA) 2 (34581522545).jpg|Dugway geode from Utah
+|-
-Fairburn Agate (ultimately derived from the Minnelusa Formation, Pennsylvanian-Permian; collected east of the Black Hills, western South Dakota, USA) 26 (32406082220).jpg|Fairburn agate from western South Dakota
+| German agate || Near Idar-Oberstein, Germany || Europe || Often red or pink, sometimes other colors || [[#Nodular agate|Nodular agate]] || Volcanic rock || Permian period || [[File:Agate-MCG 91225-P4150832-white.jpg|thumb|center|German agate from Idar-Oberstein]] || <ref name="pabian" />{{rp|pp=52–55}}
-LagunaAgateFromMexico.jpg|Laguna agate
+|-
-Agate nodule ("Lake Superior Agate") (floor of Lake Superior, offshore Keweenaw Peninsula, Michigan USA) 2 (33741645898).jpg|Rough Lake Superior agate from [[Keweenaw Peninsula]], Michigan
+| Scottish agate || [[Stonehaven]] to just south of [[Ayr]], near [[Oban]], and surrounding the [[Cheviot Hills]], Scotland, United Kingdom || Europe || Various colored bands || [[#Nodular agate|Nodular agate]] || Volcanic rock (andesite) || [[Early Devonian]] period || [[File:Agate detail, Scotland 007 (cropped).jpg|thumb|center|Close-up of a Scottish agate from [[Ayrshire]]]] || <ref name="pabian" />{{rp|pp=58-61}}
-Thunder Egg Agate (Priday Blue Bed, John Day Formation, Miocene; near Madras, Oregon, USA) 3 (33992544563).jpg|Thunder egg from Oregon
+|-
-Holley Blue Agate (Linn County, Oregon, USA) 9.jpg|Holley blue agate from Oregon
+| Small Isles agate || Islands off the west coast of Scotland, United Kingdom || Europe || Various colored bands || [[#Nodular agate|Nodular agate]] || Volcanic rock (basalt) || [[Tertiary (period)|Tertiary]] period || || <ref name="pabian" />{{rp|pp=58-61}}
-Elimia fossils Wyoming.jpg|alt=An irregular dark stone with a flat polished front; many white fragments of elongated, spiral, "corkscrew" shells seem to float in the dark stone|Turritella agate (''Elimia tenera'')
+|-
-Chalcedony (Variety Agate)-262773.jpg|Agate from British Columbia
+| Potato stone (Pot stone) || [[Bristol]] and [[Somerset]], England, United Kingdom || Europe || Irregularly-shaped, reddish, banded agate nodules, typically surrounding a hollow cavity lined with macroscopic quartz, but sometimes completely filled || [[#Nodular agate|Nodular agate]] || Sedimentary rock (dolomitic [[Conglomerate (geology)|conglomerate]] and [[marl]]) || [[Triassic]] period || [[File:Quartz-agate (12250382174).jpg|thumb|center|Potato stone from England]] || <ref name="pabian" />{{rp|pp=72}}
-</gallery>
+|-
+| {{anchor|Boley agate}}Boley agate || Central [[Oklahoma]], United States || North America || White fortification and eye banding with clasts of brecciated chert || [[#Vein agate|Vein agate]] || Sedimentary rock (Boley conglomerate layer, Vamoosa formation) || [[Virgilian series]] || || <ref>{{cite journal |last1=Suneson |first1=Neil H. |last2=Lyon |first2=William G. |last3=Goza |first3=David |title=Boley Agate — Chert Breccia Clasts In The Vamoosa Formation |journal=Shale Shaker |date=July–August 2013 |volume=64 |issue=1 |pages=22–37 |url=http://www.ogs.ou.edu/geology/pdf/BOLEYAGATEnhs.pdf |access-date=27 July 2025}}</ref>
-=== South America ===
+|-
-* ''Brazilian agate'' is probably one of the largest agates. They can reach {{convert|0.9|m|ft|abbr=on}} in diameter and weigh over {{convert|120|kg|lb|abbr=on}}. Brazilian agate is found primarily as nodules and geodes in decomposed volcanic ash and basalt of [[Lopingian|Late Permian]] age. The largest deposits are in the Brazilian state of [[Rio Grande do Sul]], but significant amounts can also be found throughout southeastern [[Brazil]]. Some specimens can be very colorful and include features such as eyes, tubes, dendrites, and sagentite. However, most Brazilian agate that is mined is naturally pale yellow, gray, or colorless and artificially dyed before being brought to market.
+| {{anchor|Coldwater agate}}Coldwater agate (Lake Michigan cloud agate) || Great Lakes Region, United States|| North America || Banded lines of grey and white chalcedony || [[#Nodular agate|Nodular agate]] || Sedimentary rock (marine limestone and dolomite) || || || <ref>{{Cite book|last=Garvin|first=Paul|url=https://books.google.com/books?id=3a1XkpBGdAcC&q=Coldwater+agates&pg=PA65|title=Iowa's Minerals: Their Occurrence, Origins, Industries, and Lore|date=2010-09-13|publisher=University of Iowa Press|isbn=978-1-60938-014-4|language=en|access-date=2020-10-29|archive-date=2023-08-26|archive-url=https://web.archive.org/web/20230826164756/https://books.google.com/books?id=3a1XkpBGdAcC&q=Coldwater+agates&pg=PA65|url-status=live}}</ref>
-* [[Condor agate|''Condor agates'']] are found in the [[Mendoza Province|Mendoza]] province of [[Argentina]]. They typically have bright red and yellow fortification banding and may contain mossy or sagenitic inclusions. Other varieties of agate can also be found in the [[Patagonia]] area of Argentina, including ''crater agate'' (typically hollow nodules with black and red bands) and ''puma agate'' (agatized coral).
+|-
-* [[Uruguay]] was the first major source of agates in South America. Agates were discovered there in 1830, but sources in neighboring Brazil became more popular in the late 19th and 20th centuries.
+| {{anchor|Crazy lace agate}}Crazy lace agate || Mexico || North America || Brightly colored lace agate, typically white and red, sometimes yellow and grey || [[#Vein agate|Vein agate]] || Sedimentary rock || Late [[Cretaceous]] period || [[File:Crazy Lace Agate - Macro Panorama.jpg|thumb|center|Crazy lace agate]] || <ref>{{Cite book|last1=Atkinson|first1=Bill|url=https://books.google.com/books?id=ZSP94tREw7AC&q=Crazy+lace+agate&pg=PA165|title=Within the Stone: Photography|last2=Ackerman|first2=Diane|date=2004|publisher=BrownTrout Publishers|isbn=978-0-7631-8189-5|language=en|access-date=2020-10-29|archive-date=2023-08-26|archive-url=https://web.archive.org/web/20230826164751/https://books.google.com/books?id=ZSP94tREw7AC&q=Crazy+lace+agate&pg=PA165|url-status=live}}</ref><ref name="pabian" />{{rp|p=121}}
-* Agates have also been found in [[Chile]] and [[Peru]].<ref name="pabian" />{{rp|pp=122–131}}
+|-
+| {{anchor|Dugway geode}}Dugway geode || [[Utah]], United States || North America || Light grey to blue, often contain hollow cavities lined with drusy quartz || [[#Nodular agate|Nodular agate]] ([[Thunderegg|thunder egg]]) || || || [[File:Dugway Geode (Juab County, Utah, USA) 2 (34581522545).jpg|thumb|center|Dugway geode from Utah]] || <ref name="pabian" />{{rp|p=92}}
-<gallery mode="packed" heights="130px">
+|-
-Brazilian agate section (detail).JPG|Natural Brazilian agate
+| [[Fairburn agate]] || [[South Dakota]] and [[Nebraska]], United States || North America || Red fortification banding || [[#Nodular agate|Nodular agate]] || Sedimentary rock (marine carbonate sediments) || [[Pennsylvanian (geology)|Pennsylvanian]] period || [[File:Fairburn Agate (ultimately derived from the Minnelusa Formation, Pennsylvanian-Permian; collected east of the Black Hills, western South Dakota, USA) 26 (32406082220).jpg|thumb|center|Fairburn agate from western South Dakota]] || <ref>{{cite web |title=Fairburn Agate |url=https://www.mindat.org/min-1441.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=16 February 2025}}</ref><ref name="pabian" />{{rp|p=77}}
-agat, Brazylia.jpg|Dyed Brazilian agate
+|-
-Argentina001.jpg|Condor agate
+| {{anchor|Laguna agate}}Laguna agate || Ojo Laguna, [[Chihuahua (state)|Chihuahua]], Mexico || North America || Vibrant bands in shades of red, orange, pink, or purple, often exhibit parallax or shadow banding, inclusions common || [[#Nodular agate|Nodular agate]] || Volcanic rock (andesite) || [[Tertiary period|Tertiary]] period || [[File:LagunaAgateFromMexico.jpg|thumb|center|Laguna agate]] || <ref>{{Cite web |title=Laguna Agate |url=https://www.mindat.org/min-7611.html |access-date=2025-02-16 |website=www.mindat.org}}</ref><ref name="pabian" />{{rp|pp=114–115}}
-Achat 1.jpg|Agate from Uruguay
+|-
-</gallery>
+| [[Lake Superior agate]] || Near [[Lake Superior]], United States and Canada || North America || Bands in shades of red, orange, yellow, brown, white, and grey, level banding and various structural features common || [[#Nodular agate|Nodular agate]] || Volcanic rock (basalt) || Late [[Precambrian]] || [[File:Agate nodule ("Lake Superior Agate") (floor of Lake Superior, offshore Keweenaw Peninsula, Michigan USA) 2 (33741645898).jpg|thumb|center|Rough Lake Superior agate from [[Keweenaw Peninsula]], Michigan]] || <ref>{{cite web |title=Lake Superior Agate |url=https://www.mindat.org/min-9253.html |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=16 February 2025}}</ref><ref name="lynch whole book">{{Cite book |last1=Lynch |first1=Dan R. |title=Lake Superior Agates Field Guide |last2=Lynch |first2=Bob |date=2012 |publisher=Adventure Publications |isbn=978-1-59193-282-6}}</ref><ref name="pabian" />{{rp|pp=83–84}}
+|-
+| {{anchor|Lysite agate}}Lysite agate || Lysite Mountain, [[Fremont County, Wyoming]], United States || North America || Colorful bands with plumes and moss || [[#Vein agate|Vein agate]] || Sedimentary rock (marine origin) || || || <ref name="pabian" />{{rp|p=79}}
+|-
+| Blue Bed (Pony Butte) thunder egg || Richardson Ranch (formerly Priday Ranch), northeast of [[Madras, Oregon]], United States || North America || Blue and white banding with dark brown shell, frequently level-banded || [[#Nodular agate|Nodular agate]] ([[thunder egg]]) || Volcanic rock (John Day Formation, [[Rhyolite|rhyolitic]] volcanic ash) || [[Miocene]] epoch || [[File:Thunder Egg Agate (Priday Blue Bed, John Day Formation, Miocene; near Madras, Oregon, USA) 3 (33992544563).jpg|thumb|center|Blue Bed thunder egg from near Madras, Oregon]] || <ref name="pabian" />{{rp|p=99}}
+|-
+| {{anchor|Holley blue agate|Holly blue agate}}Holley (Holly) blue agate || Near [[Holley, Oregon]] || North America || Lavender to blue || [[#Nodular agate|Nodular agate]] || || || [[File:Holley Blue Agate (Linn County, Oregon, USA) 9.jpg|thumb|center|Holley blue agate from Oregon]] || <ref name="pabian" />{{rp|p=103}}
+|-
+| {{anchor|Sweetwater agate}}Sweetwater agate || Near [[Sweetwater River (Wyoming)|Sweetwater River]], [[Wyoming]] || North America || Small moss agates with brown or black dendrites, fluorescent under [[Ultraviolet|UV]] light || [[#Nodular agate|Nodular agate]] || Sedimentary rock (sandstone) || Miocene epoch || || <ref name="pabian" />{{rp|p=79}}
+|-
+| [[Elimia tenera|Turritella agate]] || Wyoming || North America || Brown fossil agate with the elongated spiral shells of an extinct freshwater snail (Elimia tenera) || [[#Fossil agate|Fossil agate]] || Sedimentary rock ([[Green River Formation]]) || [[Eocene]] epoch || [[File:Elimia fossils Wyoming.jpg|thumb|center|alt=An irregular dark stone with a flat polished front; many white fragments of elongated, spiral, "corkscrew" shells seem to float in the dark stone|Turritella agate (''Elimia tenera'')]] || <ref name="turritella">{{Cite web |last=King |first=Hobart M. |title=Turritella Agate |url=https://geology.com/gemstones/turritella/ |access-date=16 February 2025 |website=geology.com}}</ref>
+|-
+| {{anchor|Brazilian agate}}Brazilian agate || [[Rio Grande do Sul]] and other southeastern states, Brazil || South America || Often large, up to {{convert|0.9|m|ft|abbr=on}} in diameter and over {{convert|120|kg|lb|abbr=on}}, commonly pale yellow, gray, or colorless (usually sold artificially dyed), are more colorful or contain structural features || [[#Nodular agate|Nodular agate]] || Volcanic rock (decomposed volcanic ash and basalt) || Late Permian period || [[File:Brazilian agate section (detail).JPG|thumb|center|Natural Brazilian agate]] [[File:5agat, Brazylia.jpg|thumb|center|Dyed Brazilian agate]] || <ref name="pabian" />{{rp|pp=122–126}}
+|-
+| [[Condor agate]] || [[Mendoza Province|Mendoza]], Argentina || South America || Bright red and yellow fortification banding, may contain mossy or sagenitic inclusions || [[#Nodular agate|Nodular agate]] || || || [[File:Argentina001.jpg|thumb|center|Condor agate]] || <ref name="pabian" />{{rp|pp=129–131}}
+|-
+| {{anchor|Crater agate}}Crater agate || [[Patagonia]], Argentina || South America || Typically hollow, black with red bands near the center || [[#Nodular agate|Nodular agate]] || Volcanic rock (rhyolite) || [[Jurassic]] period || || <ref name="pabian" />{{rp|p=131}}
+|-
+| {{anchor|Puma agate}}Puma agate || [[Andes]], Patagonia, Argentina || South America || Agatized coral || [[#Fossil agate|Fossil agate]] || Sedimentary rock (marine) || || || <ref name="pabian" />{{rp|p=131}}
+|}
 == Uses ==
-Agate has long been popular as a [[gemstone]] in [[jewelry]] such as [[pins]], [[brooch]]es, [[necklaces]], [[earrings]], and [[bracelets]]. Agates have also historically been used in the art of [[hardstone carving]] to make knives, [[inkstand]]s, [[seal (emblem)|seals]], [[marbles]], and other objects. Today, they are still used to make beads, decorative displays, carvings, and [[cabochons]], as well as face-polished and tumble-polished specimens of varying size and origin. Agate collecting is a popular hobby, and agate specimens can be found in numerous gift shops, museums, galleries, and private collections.<ref name="pabian" />{{rp|pp=159–168}}
+Agate is frequently used as a gemstone in [[jewelry]] such as [[pins]], [[brooch]]es, [[necklaces]], [[earrings]], and [[bracelets]]. Agates have also historically been used in the art of [[hardstone carving]] to make knives, [[inkstand]]s, [[seal (emblem)|seals]], [[marbles]], and other objects. Today, they are widely used to make beads, decorative displays, carvings, and [[cabochons]], as well as face-polished and tumble-polished specimens of varying size and origin. Agate collecting is a popular hobby, and agate specimens can be found in numerous gift shops, museums, galleries, and private collections.<ref name="pabian" />{{rp|pp=159–168}}
-Industrial uses of agate exploit its hardness, ability to retain a highly polished surface finish and resistance to chemical attack. Historically, it was used to make bearings for highly accurate [[laboratory balance]]s and [[Mortar and pestle|mortars and pestles]] to crush and mix chemicals. During the [[Second World War]], black agate beads mined from [[Queensland, Australia]] were used in the turn and bank indicators of military aircraft.<ref name="pabian" />{{rp|pp=168–169}}
+Industrial uses of agate exploit its hardness, ability to retain a highly polished surface finish and resistance to chemical attack. Historically, it was used to make bearings for highly accurate [[laboratory balance]]s and [[Mortar and pestle|mortars and pestles]] to crush and mix chemicals. During the [[Second World War]], black agate beads mined from [[Queensland]], Australia were used in the turn and bank indicators of military aircraft.<ref name="pabian" />{{rp|pp=168–169}}
-Agates, particularly moss agates, were first used during the [[Stone Age]] to make tools such as arrow and spear points, needles, and hide scrapers. Artefacts from as early as 7000 BCE have been found in [[Mongolia]], and the [[Natufian]] people of the [[Levant]] are known to have made knives and arrowheads from moss agate as early as 10000 BCE. Agate jewelry from [[Sumeria]] has been dated to c. 2500 BCE, and the [[Ancient Egyptians]], [[Mycenaeans]], and [[Ancient Rome|Romans]] all used agate in their jewelry.<ref name="pabian" />{{rp|pp=159–163}} Archaeological recovery at the [[Knossos]] site on [[Crete]] illustrates the role of agates in [[Bronze Age]] [[Minoan civilization|Minoan]] culture.<ref>C. Michael Hogan. 2007. [http://www.themodernantiquarian.com/site/10854/knossos.html#fieldnotes ''Knossos fieldnotes'', Modern Antiquarian] {{Webarchive|url=https://web.archive.org/web/20180711201424/http://www.themodernantiquarian.com/site/10854/knossos.html#fieldnotes |date=2018-07-11 }}</ref> The ornamental use of agate was common in [[ancient Greece]], in assorted [[jewelry]] and in the [[seal stone]]s of Greek warriors.<ref>{{cite magazine |date=7 November 2017 |title=Masterpiece of Greek Art Found in the Griffin Warrior Tomb |url=https://smithsonianmag.com/smart-news/masterpiece-greek-art-found-griffin-warrior-tomb-180967141 |magazine=[[Smithsonian (magazine)|Smithsonian]] |publisher=[[Smithsonian Institution]]}}</ref>
+Agates, particularly moss agates, were first used during the [[Stone Age]] to make tools such as arrow and spear points, needles, and hide scrapers. Artifacts from as early as 7000 BCE have been found in Mongolia, and the [[Natufian]] people of the [[Levant]] are known to have made knives and arrowheads from moss agate as early as 10000 BCE. Agate jewelry from [[Sumeria]] has been dated to c. 2500 BCE, and the [[Ancient Egyptians]], [[Mycenaeans]], and [[Ancient Rome|Romans]] all used agate in their jewelry.<ref name="pabian" />{{rp|pp=159–163}} Archaeological recovery at the [[Knossos]] site on [[Crete]] illustrates the role of agates in [[Bronze Age]] [[Minoan civilization|Minoan]] culture.<ref>C. Michael Hogan. 2007. [http://www.themodernantiquarian.com/site/10854/knossos.html#fieldnotes ''Knossos fieldnotes'', Modern Antiquarian] {{Webarchive|url=https://web.archive.org/web/20180711201424/http://www.themodernantiquarian.com/site/10854/knossos.html#fieldnotes |date=2018-07-11 }}</ref> The ornamental use of agate was common in [[ancient Greece]], in assorted jewelry and in the [[seal stone]]s of Greek warriors.<ref>{{cite magazine |date=7 November 2017 |title=Masterpiece of Greek Art Found in the Griffin Warrior Tomb |url=https://smithsonianmag.com/smart-news/masterpiece-greek-art-found-griffin-warrior-tomb-180967141 |magazine=[[Smithsonian (magazine)|Smithsonian]] |publisher=[[Smithsonian Institution]]}}</ref>
-[[Idar-Oberstein]] was a historically important location in Germany that made use of agate on an industrial scale, dating back to c. 1375 CE.<ref name="pabian" />{{rp|p=52}} Originally, locally found agates were used to make all types of objects for the European market, but it became a globalized business around the turn of the 20th century. Idar-Oberstein began to import large quantities of agate from Brazil, as ship's ballast. Making use of a variety of proprietary chemical processes, they produced colored beads that were sold around the globe.<ref>{{Cite web |url=http://www.farlang.com/art/2007-04-15.7721093142 |title=Background Article on Idar Oberstein |access-date=2008-11-27 |archive-date=2008-12-23 |archive-url=https://web.archive.org/web/20081223064824/http://www.farlang.com/art/2007-04-15.7721093142 |url-status=live }}</ref>
+Idar-Oberstein was a historically important location in Germany that made use of agate on an industrial scale, dating back to c. 1375 CE.<ref name="pabian" />{{rp|p=52}} Originally, locally found agates were used to make all types of objects for the European market, but it became a globalized business around the turn of the 20th century. Idar-Oberstein began to import large quantities of agate from Brazil, as ship's ballast. Making use of a variety of proprietary chemical processes, they produced colored beads that were sold around the globe.<ref>{{Cite web |url=http://www.farlang.com/art/2007-04-15.7721093142 |title=Background Article on Idar Oberstein |access-date=2008-11-27 |archive-date=2008-12-23 |archive-url=https://web.archive.org/web/20081223064824/http://www.farlang.com/art/2007-04-15.7721093142 |url-status=live }}</ref>
 <gallery mode="packed" heights="130px">
@@ Line 188: / Line 181: @@
 File:Byzantine - The "Rubens Vase" - Walters 42562.jpg|The "[[Rubens Vase]]" ([[Byzantine Empire]]). Carved in high relief from a single piece of agate, most likely created in an imperial workshop for a Byzantine emperor.
 File:Victorian banded agate ear rings.jpg|Victorian banded agate earrings
-File:Maryland Agate.jpg|Patuxent River stone from Maryland — cut and illuminated from behind as a [[nightlight]]
+File:Maryland Agate.jpg|[[Patuxent River]] stone from Maryland — cut and illuminated from behind as a [[nightlight]]
 File:唐-玛瑙兽首杯.jpg|Agate [[drinking horn]], [[Tang dynasty]]
 </gallery>
-==Health impact==
+== Treatment and processing ==
-Respiratory diseases such as [[silicosis]], and a higher [[Cumulative incidence|incidence]] of [[tuberculosis]] among workers involved in the agate industry, have been studied in [[India]] and China.<ref>{{cite journal |last1=Chaudhury |first1=Nayanjeet |last2=Phatak |first2=Ajay |last3=Paliwal |first3=Rajiv |title=Co-morbidities among silicotics at Shakarpur: A follow up study |journal=Lung India |volume=29 |issue=1 |pages=6–10 |doi=10.4103/0970-2113.92348 |pmc=3276038 |pmid=22345906 |date=January 2012 |doi-access=free }}</ref><ref>{{cite journal |last1=Jiang |first1=CQ |last2=Xiao |first2=LW |last3=Lam |first3=TH |last4=Xie |first4=NW |last5=Zhu |first5=CQ |title=Accelerated silicosis in workers exposed to agate dust in Guangzhou, China. |journal=American Journal of Industrial Medicine |date=July 2001 |volume=40 |issue=1 |pages=87–91 |pmid=11439400 |doi=10.1002/ajim.1074}}</ref><ref>{{cite journal |last1=Tiwari |first1=RR |last2=Narain |first2=R |last3=Sharma |first3=YK |last4=Kumar |first4=S |title=Comparison of respiratory morbidity between present and ex-workers of quartz crushing units: Healthy workers' effect |journal=Indian Journal of Occupational and Environmental Medicine |date=September 2010 |volume=14 |issue=3 |pages=87–90 |pmid=21461160 |doi=10.4103/0019-5278.75695 |pmc=3062020 |doi-access=free }}</ref>
+[[File:Agate, physical properties and origin (Plate VII) BHL48235765.jpg|thumb|Composite image of an agate slice showing natural color at the top and various artificial colors below]]
+Many pale or dull agates are artificially treated to enhance their colors and make them more appealing to consumers. Chalcedony is one of the earliest stones to be artificially enhanced,<ref name="russell">{{cite web |last1=Russell |first1=Daniel |title=Historic Methods of Artificially Coloring Agates |url=https://www.mindat.org/article.php/170/Historic+Methods+of+Artificially+Coloring+Agates |website=mindat.org |publisher=Hudson Institute of Mineralogy |access-date=8 September 2025 |date=13 January 2008}}</ref> with heating having been used for centuries to produce the rich red color of carnelian.<ref name="treated gem">{{cite web |title=treated gem |url=https://www.britannica.com/art/treated-gem |website=Encyclopedia Britannica |access-date=8 September 2025 |date=6 November 2016}}</ref> Many varieties of chalcedony, including agate, are relatively porous and absorb [[dye]]s well.<ref name="russell" /><ref name="treated gem" /> The classical methods<ref name="color loss">{{cite journal |last1=de Almeida Silva |first1=Rodrigo |last2=Petter |first2=Carlos Otavio |last3=Schneider |first3=Ivo André H. |title=Avaliação da perda da coloração artificial de ágatas |journal=Rem: Revista Escola de Minas |date=September 2007 |volume=60 |issue=3 |pages=477–482 |doi=10.1590/S0370-44672007000300007 |url=https://www.scielo.br/j/rem/a/ZmDd64KZTchSBcfXtGKPxvm|hdl=10183/10181 |hdl-access=free }}</ref> of staining agates were developed in the early 19th century in Idar-Oberstein, Germany. After the agates were cut and cleaned, they were soaked for several days in a particular inorganic dye or sugar solution depending on the desired color to be achieved. This was often followed by an acid bath and/or heating ("burning") to [[oxidize]] the compounds:<ref name="russell" />
+* Blue agates were produced by using a solution of [[potassium ferricyanide]] or [[Potassium ferrocyanide|ferrocyanide]] followed by [[iron sulfate]], which forms [[Prussian blue|iron ferricyanide (Prussian blue)]].<ref name="russell" />
+* Red agates were produced either by burning alone, or if not enough natural iron was present in the stones, by first soaking them in a solution of [[iron nitrate]] and then burning them to form [[iron oxide]].<ref name="russell" />
+* Green agates were produced using solutions of [[nickel]] or [[chromium]] [[Salt (chemistry)|salts]] followed by burning.<ref name="russell" />
+* Black agates were produced by soaking the stones in a sugar solution and then immersing them in [[sulfuric acid]] to carbonize the sugars;<ref name="russell" /> brown agates can also be produced using a similar method.<ref name="treated gem" />
+* Yellow agates can be produced using hydrochloric acid followed by burning.<ref name="treated gem" />
+Organic [[aniline]] dyes derived from [[coal tar]] began to be used later in the 19th century,<ref name="russell" /> which allowed for the production of agates of additional colors such as pink and purple. While the colors produced by the classical methods are typically permanent, the colors produced by organic dyes can fade with exposure to light or heat.<ref name="color loss" /> Organic dyes can also only penetrate a short distance into the agate from the exposed surfaces. The practice of artificially treating agates remains popular today, and dyed Brazilian agates in particular are very common on the global market.<ref name="pabian" />{{rp|p=157}}
+Larger agates are often cut into halves or slices with circular diamond saws. They can then be polished with lapidary grinding, sanding, and polishing wheels of successively greater grit sizes.<ref name="pabian" />{{rp|pp=151–155}} Smaller agates and crushed agate fragments can alternatively be polished using [[Tumble finishing|rock tumblers]] or vibratory polishers. This equipment can generate large quantities of silica dust. Respiratory diseases such as [[silicosis]], and a higher [[Cumulative incidence|incidence]] of [[tuberculosis]] among workers involved in the agate industry, have been studied in India and China.<ref>{{cite journal |last1=Chaudhury |first1=Nayanjeet |last2=Phatak |first2=Ajay |last3=Paliwal |first3=Rajiv |title=Co-morbidities among silicotics at Shakarpur: A follow up study |journal=Lung India |volume=29 |issue=1 |pages=6–10 |doi=10.4103/0970-2113.92348 |pmc=3276038 |pmid=22345906 |date=January 2012 |doi-access=free }}</ref><ref>{{cite journal |last1=Jiang |first1=CQ |last2=Xiao |first2=LW |last3=Lam |first3=TH |last4=Xie |first4=NW |last5=Zhu |first5=CQ |title=Accelerated silicosis in workers exposed to agate dust in Guangzhou, China. |journal=American Journal of Industrial Medicine |date=July 2001 |volume=40 |issue=1 |pages=87–91 |pmid=11439400 |doi=10.1002/ajim.1074}}</ref><ref>{{cite journal |last1=Tiwari |first1=RR |last2=Narain |first2=R |last3=Sharma |first3=YK |last4=Kumar |first4=S |title=Comparison of respiratory morbidity between present and ex-workers of quartz crushing units: Healthy workers' effect |journal=Indian Journal of Occupational and Environmental Medicine |date=September 2010 |volume=14 |issue=3 |pages=87–90 |pmid=21461160 |doi=10.4103/0019-5278.75695 |pmc=3062020 |doi-access=free }}</ref>
 ==See also==
@@ Line 199: / Line 203: @@
 * {{annotated link|List of minerals}}
 {{clear}}
+== Notes ==
+{{notelist}}
 == References ==
 {{Reflist}}
@@ Line 214: / Line 222: @@
 [[Category:Gemstones]]
 [[Category:Hardstone carving]]
-[[Category:Silicate minerals]]
 [[Category:Symbols of Florida]]
 [[Category:Provincial symbols of Nova Scotia]]

Agate: Difference between revisions

Latest revision as of 22:25, 19 November 2025

Etymology

Composition

Formation

Structural varieties

Wall-banded agates

Level-banded agates

Regional varieties

Uses

Treatment and processing

See also

Notes

References

External links

Navigation menu

Search