View source for Peridot

{{short description|Green gem-quality mineral}}
{{other uses}}
{{Infobox mineral
| name   =   Peridot
| category    = [[Silicate mineral]]s
| boxwidth    = 
| boxbgcolor  = #acdf7d
| image       = Forsterite-Olivine-tmu14a.jpg
| image size  = 
| caption     = 
| formula     = {{chem2|(Mg,Fe)2SiO4}}
| molweight   = 
| color       = Yellow, to [[chartreuse (color)|yellow-green]], [[olive (color)|olive-green]], to brownish, sometimes a [[lime (color)|lime green]], to emerald hue
| habit       = 
| system      = [[orthorhombic crystal system|Orthorhombic]]
| twinning    = Uncommon, simple twinning can occur on {100}, {011},{012}, cyclic twinning on {031} 
| cleavage    = Poor on {010} and {110}, {010} cleavage improves with increasing iron content
| fracture    = [[conchoidal fracture|Conchoidal]]
| mohs        = 6.5–7
| luster      = Vitreous to oily
| refractive  = 1.64–1.70 
| opticalprop = 
| birefringence = +0.036
| pleochroism = Weak pale yellow-green to yellow, yellow to yellow orange
| streak      = Colorless
| gravity     = 3.2–4.3
| melt        = between 1,200 and 1,900°[[celsius|C]]
| fusibility  = Infusible avoid thermal shock 
| diagnostic  = 
| solubility  = Slowly forms gelatinous silica in {{chem2|H Cl}}
| diaphaneity = Translucent to transparent 
| other       = 
}}

'''Peridot''' ({{IPAc-en|ˈ|p|ɛ|r|ɪ|ˌ|d|ɒ|t|}} {{respell|PERR|ih|dot|}}), sometimes called '''chrysolite''', is a [[lime (color)|yellow-green]] transparent variety of [[olivine]]. Peridot is one of the few [[gemstone]]s that occur in only one color.

Peridot can be found in [[mafic]] and [[ultramafic rock]]s occurring in [[lava]] and [[peridotite]] [[xenolith]]s of the [[mantle (geology)|mantle]]. The gem occurs in silica-deficient rocks such as volcanic [[basalt]] and [[pallasite|pallasitic]] [[meteorite]]s. Along with [[diamonds]], peridot is one of only two gems observed to be formed not in [[Earth's crust]], but in the molten rock of the upper mantle.<ref name="Rock & Gem Magazine 2023">{{cite magazine |title=Peridot crystals: Formation & locations |magazine=Rock & Gem Magazine |date=2023-07-10 |quote=Get to know this August birthstone |url=https://www.rockngem.com/peridot-crystals/ |via=rockngem.com |access-date=2024-01-21 |df=dmy-all }}</ref> Gem-quality peridot is rare on Earth's surface due to its susceptibility to alteration during its movement from deep within the mantle and weathering at the surface.<ref name="The University of Texas at Austin Gems">{{cite web | title=Peridot |department=Gem notes |id=course&nbsp;347k |website=geo.utexas.edu |publisher=[[UT-Austin|The University of Texas]] |place=Austin, TX |series=Geology Department |url=https://www.geo.utexas.edu/courses/347k/redesign/Gem_Notes/Peridot/peridot_main.htm |access-date=2024-01-21 }}</ref> Peridot has a [[chemical formula]] of {{nobr| {{chem2|(Mg,Fe)2SiO4}}}}.

Peridot is one of the [[birthstone]]s for the month of August.<ref>{{cite periodical |title=Color, meanings, and symbolism [of] August birthstone peridot |periodical=[[Old Farmer's Almanac]] |via=almanac.com |url=https://almanac.com/august-birthstone-color-and-meaning }}</ref>

==Etymology==
The origin of the name ''peridot'' is uncertain. The ''[[Oxford English Dictionary]]'' suggests an alteration of [[English language|Anglo]]–[[Norman language|Norman]] {{lang|xno|pedoretés}} (classical [[Latin]] {{lang|la|pæderot}}-), a kind of [[opal]], rather than the [[Arabic]] word {{lang|ar-Latn|faridat}}, meaning "[[gemstone]]".

The ''[[Middle English Dictionary]]''{{'}}s entry on ''peridot'' includes several variations: {{lang|enm|peridod}}, {{lang|enm|peritot}}, {{lang|enm|pelidod}} and {{lang|enm|pilidod}} — other variants substitute ''y'' for letter ''i'' used here.<ref>{{cite dictionary |first=Sherman M. |last=Kuhn |year=1982 |title=peridot |dictionary=[[Middle English Dictionary]] |title-link= |publisher=University of Michigan Press |isbn=0-472-01163-4 |page=[https://books.google.com/books?id=XR52pY68WOUC&pg=PA818 818&nbsp;ff] |url=https://books.google.com/books?id=XR52pY68WOUC&pg=PA818   |via=Google books }}</ref>

The earliest use of the word in [[English language|English]] is possibly in the 1705 register of the [[St Albans Cathedral|St.&nbsp;Albans Abbey]]: The dual entry is in Latin with the translation to English listed as ''peridot''. It records that on his death in 1245, Bishop John bequeathed various items, including peridot gems, to the Abbey.<ref>{{cite book |first=James, Sir |last=Ware |year=1705 |title=The Antiquities and History of Ireland |publisher=A. Crook |page=628&nbsp;ff |url=https://books.google.com/books?id=gjrnAAAAMAAJ&pg=PA628 |via=Google books }}</ref>

==Appearance==
Peridot is one of the few gemstones that occur in only one color: an [[olive-green]]. The intensity and tint of the green, however, depends on the percentage of [[iron]] in the crystal structure, so the color of individual peridot gems can vary from yellow, to olive, to brownish-green. In rare cases, peridot may have a medium-dark toned, pure green with no secondary yellow hue or brown mask. Lighter-colored gems are due to lower [[iron]] concentrations.<ref>{{cite book |last=Wise |first=Richard W. |year=2016 |title=Secrets of the Gem Trade: The connoisseur's guide to precious gemstones |edition=2nd |publisher=Brunswick House Press |location=Lenox, MA |isbn=9780972822329 |page=220 }}</ref>

== Mineral properties ==

=== Crystal structure ===
[[File:Atomic_structure_of_olivine_1.png|thumb|The atomic scale structure of olivine looking along the ''a'' axis. Oxygen is shown in red, silicon in pink, and magnesium/iron in blue. A projection of the unit cell is shown by the black rectangle.]]
The molecular structure of peridot consists of isomorphic olivine, silicate, magnesium and iron in an [[orthorhombic crystal system]]. In an alternative view, the atomic structure can be described as a hexagonal, close-packed array of oxygen [[ion]]s with half of the octahedral sites occupied by magnesium or iron ions and one-eighth of the tetrahedral sites occupied by silicon ions.

=== Surface property ===
Oxidation of peridot does not occur at natural surface temperature and pressure but begins to occur slowly at {{convert|600|C|K|sigfig=2}} with rates increasing with temperature.<ref>{{cite journal |last1=Knafelc |first1=Joseph |last2=Filiberto |first2=Justin |last3=Ferré |first3=Eric C. |last4=Conder |first4=James A. |last5=Costello |first5=Lacey |last6=Crandall |first6=Jake R. |last7=Dyar |first7=M. Darby |last8=Friedman |first8=Sarah A. |last9=Hummer |first9=Daniel R. |last10=Schwenzer |first10=Susanne P. |display-authors=6 |date=May 2019 |title=The effect of oxidation on the mineralogy and magnetic properties of olivine |journal=[[American Mineralogist]] |volume=104 |issue=5 |pages=694–702 |doi=10.2138/am-2019-6829 |bibcode=2019AmMin.104..694K |s2cid=155508562 |issn=0003-004X |url=https://pubs.geoscienceworld.org/ammin/article-abstract/104/5/694/570176/The-effect-of-oxidation-on-the-mineralogy-and |via=geoscienceworld.org  |lang=en}}</ref> The oxidation of the olivine occurs by an initial breakdown of the [[fayalite]] component, and subsequent reaction with the forsterite component, to give [[magnetite]] and [[orthopyroxene]].

==Occurrence==
===Geologically===
[[Olivine]], of which peridot is a type, is a common mineral in [[mafic]] and [[ultramafic rock]]s, often found in [[lava]] and in [[peridotite]] [[xenolith]]s of the [[Mantle (geology)|mantle]], which lava carries to the surface; however, gem-quality peridot occurs in only a fraction of these settings. Peridots can also be found in meteorites.

Peridots can be differentiated by size and composition. A peridot formed as a result of volcanic activity tends to contain higher concentrations of lithium, nickel and zinc than those found in meteorites.<ref>{{cite journal |last1=Shen |first1=A. |display-authors=etal |year=2011 |title=Identification of extraterrestrial peridot by trace elements |journal=[[Gems & Gemology]] |volume=47 |issue=3 |pages=208–213 |doi=10.5741/GEMS.47.3.208 }}</ref>{{full citation|date=August 2024|reason=Needs either month or issue nr.; doi & issn etc. would be good too }}

Olivine is an abundant mineral, but gem-quality peridot is rather rare due to its [[chemical stability|chemical instability]] on Earth's surface. Olivine is usually found as small grains and tends to exist in a heavily weathered state, unsuitable for decorative use. Large crystals of [[forsterite]], the variety most often used to cut peridot gems, are rare; as a result, peridot is considered to be [[precious stone|precious]].

In the ancient world, the mining of peridot was called ''topazios'' then, on [[Zabargad Island|St.&nbsp;John's Island, in the Red Sea]] began about 300&nbsp;BCE.<ref>{{cite web |title=St.&nbsp;John's Island peridot information and history |website=[[Mindat.org]] |url=http://www.mindat.org/loc-6423.html }}</ref>

The principal source of peridot olivine today is the [[San Carlos Apache Indian Reservation]] in Arizona, US.{{efn|
"Although some good olive-colored crystals are found in a few other places, like Burma, China, Zambia, and Pakistan, ninety percent of all known peridots are found in just one place. It is a Native American reservation, and it is located in a little-visited corner of the United States: {{nobr|San Carlos." — V.&nbsp;Finlay<ref>{{cite book |last=Finlay |first=Victoria |date=August 15, 2006 |title=Jewels: A secret history |at=Kindle locations 543–546 |publisher=Ballantine Books |edition=Kindle|ISBN=978-0345493354}}</ref>}}
}}
It is also mined at another location in [[Arizona]], and in [[Arkansas]], [[Hawaii]], [[Nevada]], and [[New Mexico]] at [[Kilbourne Hole]], in the US; and in [[Australia]], [[Brazil]], [[China]], [[Egypt]], [[Kenya]], [[Mexico]], [[Myanmar]] (Burma), [[Norway]], [[Pakistan]], [[Saudi Arabia]], [[South Africa]], [[Sri Lanka]], and [[Tanzania]].{{citation needed|date=November 2021}}

===In meteorites===
[[File:NHM - Pallasit Fukang.jpg|thumb|right|Pallasite meteorite with olive-green peridot crystals, found in Fukang, China.]]
Peridot crystals have been collected from some [[pallasite]] [[meteorite]]s. The most commonly studied pallasitic peridot belongs to the Indonesian Jeppara meteorite, but others exist such as the Brenham, Esquel, Fukang, and Imilac meteorites.<ref>{{cite journal |last1=Leelawatanasuk |first1=Thanong |last2=Atichat |first2=Wilawan |last3=Thye Sun |first3=Tay |last4=Sriprasert |first4=Boontawee |last5=Jakkawanvibul |first5=Jirapit |year=2014 |title=Some characteristics of taaffeite from Myanmar |journal=The Journal of Gemmology |volume=34 |issue=2 |pages=144–148 |doi=10.15506/jog.2014.34.2.144 |issn=1355-4565}}</ref> Pallasitic (extraterrestrial) peridot differs chemically from its earthbound counterpart, in that pallasitic peridot lacks nickel.<ref>{{cite web |title=Alien sightings: Pallasite |website=stonegrouplabs.com |url=https://stonegrouplabs.com/wp-content/uploads/2021/06/0314GG-MarAprGMNPallasite.pdf |access-date= }}</ref>

==Gemology==
[[File:Peridot Doubling.jpg|thumb|alt=Due to its high birefringence, doubling of facet junctions is commonly seen when viewing peridot under magnification.|Due to its high birefringence, doubling of facet junctions is commonly seen when viewing peridot under magnification.]]
[[Orthorhombic]] minerals, like peridot, have [[biaxial]] [[birefringence]] defined by three principal axes: {{mvar|α, β}}, and {{mvar|γ}}. Refractive index readings of faceted gems can range around {{mvar|α}} = 1.651, {{mvar|β}} = 1.668, and {{mvar|γ}} = 1.689, with a biaxial positive birefringence of 0.037–0.038. With decreasing magnesium and increasing iron concentration, the specific gravity, color darkness and refractive indices increase, and the {{nobr|{{mvar|β}} index}} shifts toward the {{mvar|γ}} index. Increasing iron concentration ultimately forms the iron-rich [[Endmember|end-member]] of the olivine [[solid solution]] series [[fayalite]].<ref>{{cite journal |last=Koivula |first=John I. |year=1981 |title=San&nbsp;Carlos peridot |journal=[[Gems & Gemology]] |volume=17 |issue=4 |pages=205–214 |doi=10.5741/gems.17.4.205 |url=https://www.gia.edu/doc/San-Carlos-Peridot.pdf |via=gia.edu |access-date=14 February 2023 |lang=en}}</ref>
 
A study of Chinese peridot gem samples determined the hydro-static [[specific gravity]] to be 3.36&nbsp;. The visible-light spectroscopy of the same Chinese peridot samples showed light bands between 493.0–481.0&nbsp;nm, the strongest absorption at 492.0&nbsp;nm.<ref name=Koivula-1986>{{cite journal |last1=Koivula |first1=John I.|last2=Fryer|first2=C.W. |date=1986-04-01 |df=dmy-all |title=The gemological characteristics of Chinese peridot |journal=[[Gems & Gemology]] |volume=22 |issue=1 |pages=38–40 |doi=10.5741/GEMS.22.1.38 |issn=0016-626X |url=http://www.gia.edu/gems-gemology/spring-1986-china-peridot-koivula |url-access=subscription }}</ref>

The largest cut peridot olivine is a {{convert|310|carat|g|abbr=off|lk=in|adj=on}} specimen in the gem collection of the [[Smithsonian Museum]] in Washington, D.C.

Inclusions are common in peridot crystals but their presence depends on the location where it was found and the geological conditions that led to its crystallization.
* Primary negative crystals – rounded gas bubbles – form in situ with peridot, and are common in Hawaiian peridots.
* Secondary negative crystals form in peridot fractures.
* "Lily pad" cleavages are often seen in San&nbsp;Carlos peridots, and are a type of secondary negative crystal. They can easily be seen under reflected light as circular discs surrounding a negative crystal.
* Silky and rod-like inclusions are common in Pakistani peridots.<ref>{{cite web |title=Sapat Gali, Naran, Kaghan Valley, Mansehra District, Khyber Pakhtunkhwa Province, Pakistan |website=[[mindat.org]] |url=https://www.mindat.org/loc-2536.html }}</ref>
* The most common mineral inclusion in peridot is the chromium-rich mineral [[chromite]].
* Magnesium-rich minerals also can exist in the form of [[pyrope]] and [[magnesiochromite]]. These two types of mineral inclusions are typically surrounded "lily-pad" cleavages. 
* Biotite flakes appear flat, brown, translucent, and tabular.<ref>{{cite dictionary |chapter=Biotite as inclusions |dictionary=Dictionary of Gems and Gemology |year=2009 |pages=87 |publisher=Springer |isbn=978-3-540-72795-8 |doi=10.1007/978-3-540-72816-0_2288 |chapter-url=https://link.springer.com/referenceworkentry/10.1007/978-3-540-72816-0_2288 }}</ref>

== Cultural history ==
Peridot has been prized since the earliest civilizations for its claimed protective powers to drive away fears and nightmares, according to superstitions. There is a superstition that it carries the gift of "inner radiance", sharpening the mind and opening it to new levels of awareness and growth, helping one to recognize and realize one's destiny and spiritual purpose.{{Citation needed|date=July 2025}}

Peridot olivine is the [[birthstone]] for the month of August.<ref>{{cite web |title=Birthstones for each month |website=gia.edu |publisher=[[Gemological Institute of America]] |url=https://www.gia.edu/birthstones |access-date=5 February 2021}}</ref>

Peridot has often been mistaken for [[emerald]] [[beryl]] and other green gems.<ref>{{cite web |title=Peridot gem guide and properties chart |website=Gemstones.com |url=https://www.gemstones.com/gemopedia/peridot |access-date=2022-09-14 |lang=en}}</ref> Noted [[gemologist]] [[George Frederick Kunz|G.F. Kunz]] discussed the confusion between [[beryl]] and peridot in many [[Relic#Christianity|church treasure]]s, most notably the "[[Shrine of the Three Kings|Three Magi]] treasure" in the [[Cologne Cathedral|Dom]] of [[Cologne]], Germany.<ref name="Kunz 1971">{{cite book | last=Kunz | first=G.F. |author-link=George Frederick Kunz | date=June 1971 | title=The Curious Lore of Precious Stones | publisher=Dover Publications | publication-place=New York, NY | isbn=0-486-22227-6 | page=66}}</ref><ref name="Rock & Gem Magazine 2023"/>

==Gallery==
<gallery mode="packed" widths="180" heights="160">
File:Peridot olivine on basalt.JPG|Peridot olivine with minor [[pyroxene]], on vesicular [[basalt]]. (field of view = 35&nbsp;mm)
File:Peridot-USGS.gif|Peridot from the San Carlos Apache Reservation in Arizona.
File:Gemperidot.JPG|Olive green peridot
File:Peridotgem.JPG|Peridot with milky inclusions
</gallery>

==Footnotes==
{{notelist}}

==References==
{{reflist|25em}}

==External links==
{{commons category|Peridot}}

* [https://www.ganoksin.com/article/lets-talk-gemstones-peridot/ Ganoksin]
* [https://www.mineralminers.com/html/perminfo.htm Mineralminers]
*[https://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/peridot.html USGS peridot data] {{Webarchive|url=https://web.archive.org/web/20181221090557/https://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/peridot.html |date=2018-12-21 }}
*[https://web.archive.org/web/20110808014635/http://www.emporia.edu/earthsci/amber/go340/peridot.htm Emporia Edu]
*[http://micro.magnet.fsu.edu/birthstones/pages/peridot.html Florida State University – Peridot]

{{Gemstone}}
{{Jewellery|state=collapsed}}
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[[Category:Gemstones]]
[[Category:Silicate minerals]]