View source for Azurite

{{Short description|Copper carbonate mineral}}
{{About|the carbonate mineral|the FDPSO vessel|Azurite FDPSO|the green fluorescent protein derivative|Green fluorescent protein#GFP derivatives|the mountain|Azurite Peak}}
{{Other uses|Azure spar}}
{{Infobox mineral
|boxbgcolor=#0066CC| name = Azurite
| boxtextcolor = #fff
| category = [[Carbonate mineral]]
| image =  Azurite - New Nevada Lode, La Sal, Utah, USA.jpg
| imagesize   = 260px
| alt         = 
| caption = Azurite from New Nevada lode, La Sal, Utah, USA
| formula = Cu<sub>3</sub>(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>2</sub>
|IMAsymbol=Azu<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| molweight = 344.67 g/mol
| strunz = 5.BA.05
| system = [[Monoclinic]]
| class = Prismatic (2/m) <br/><small>(same [[H-M symbol]])</small>
| symmetry = ''P''2<sub>1</sub>/c
| unit cell = a = 5.01&nbsp;[[Ångstrom|Å]], b = 5.85&nbsp;Å <br/>c = 10.35&nbsp;Å; β = 92.43°; Z&nbsp;=&nbsp;2
| color = Azure-blue, dark to pale blue; pale blue in transmitted light
| habit = Massive, prismatic, stalactitic, tabular
| cleavage = Perfect on {{mset|011}}, fair on {{mset|100}}, poor on {{mset|110}}
| fracture = Conchoidal
| tenacity = brittle
| mohs = 3.5 to 4
| twinning = Rare, twin planes {{mset|{{overline|1}}01}}, {{mset|{{overline|1}}02}} or {{mset|001}}
| luster = Vitreous
| opticalprop = Biaxial (+)
| refractive = n<sub>α</sub> = 1.730 n<sub>β</sub> = 1.758 n<sub>γ</sub> = 1.838
| birefringence = δ = 0.108
| dispersion = relatively weak
| pleochroism = Visible shades of blue
| 2V = Measured: 68°, calculated: 64°
| streak = Light blue
| gravity = 3.773 (measured), 3.78 (calculated)
| melt =
| fusibility =
| diagnostic =
| solubility =
| diaphaneity = Transparent to translucent
| references = <ref name=Handbook>[http://rruff.geo.arizona.edu/doclib/hom/azurite.pdf Handbook of Mineralogy]</ref><ref name=Mindat>[http://www.mindat.org/min-447.html Mindat.org]</ref><ref name=Webmin>[http://webmineral.com/data/Azurite.shtml Webmineral.com Webmineral Data]</ref>
}}

'''Azurite''' or ''[[Azure spar]]''<ref name="kriv">''Krivovichev V. G.'' Mineralogical glossary. Scientific editor [[:uk:Булах Андрій Глібович|A. G. Bulakh]]. — St.Petersburg: St.Petersburg Univ. Publ. House. 2009. — 556 p. — ISBN 978-5-288-04863-0. ''(in Russian)''</ref>{{rp|14}} is a soft, deep-blue [[copper]] [[mineral]] produced by weathering of copper ore deposits. During the early 19th century, it was also known as '''chessylite''', after the [[Type locality (geology)|type locality]] at [[Chessy, Rhône|Chessy-les-Mines]] near [[Lyon]], [[France]].<ref name=Mindat/> The mineral, a basic [[carbonate]] with the chemical formula Cu<sub>3</sub>(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>2</sub>, has been known since ancient times, and was mentioned in [[Pliny the Elder]]'s ''[[Natural History (Pliny)|Natural History]]'' under the Greek name {{Transliteration|el|kuanos}} (κυανός: "deep blue," root of English [[cyan]]) and the Latin name ''[[Cerulean|caeruleum]]''.<ref>{{usurped|1=[https://web.archive.org/web/20051220155850/http://www.ancientlibrary.com/smith-dgra/0328.html The Ancient Library: Smith, Dictionary of Greek and Roman Antiquities, p.321, right col., under ''BLUE'']}}</ref> Copper (Cu<sup>2+</sup>) gives it its blue color.<ref>{{Cite web |title=Minerals Colored by Metal Ions |url=http://minerals.gps.caltech.edu/color_causes/Metal_Ion/index.html |access-date=2023-03-01 |website=minerals.gps.caltech.edu}}</ref>

==Mineralogy==
[[File:Azurite crystal structure.jpg|left|thumb|220px|Chemical structure of azurite. Color code: red = O, green = Cu, gray = C, white = H)]]
Azurite has the formula Cu<sub>3</sub>(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>2</sub>, with the copper(II) [[cation]]s linked to two different anions, [[carbonate]] and [[hydroxide]]. It is one of two relatively common basic copper(II) [[carbonate minerals]], the other being bright green [[malachite]]. [[Aurichalcite]] is a rare basic carbonate of copper and [[zinc]].<ref name="HurlbutKlein">{{cite book |last1=Klein |first1=Cornelis |last2=Hurlbut |first2=Cornelius S. Jr. |title=Manual of mineralogy : (after James D. Dana) |date=1993 |publisher=Wiley |location=New York |isbn=047157452X |edition=21st |pages=417–418}}</ref> Simple [[copper(II) carbonate|copper carbonate]] (CuCO<sub>3</sub>) is not known to exist in nature, due to the high affinity of the {{chem|Cu|2+}} ion for the [[hydroxide]] anion {{chem|H|O|-}}.<ref>{{Cite book|title=Principles of Corrosion Engineering and Corrosion Control|last=Ahmad|first=Zaki|date=2006|publisher=Butterworth-Heinemann|isbn=9780750659246|location=Oxford|pages=120–270}}</ref>

Azurite crystallizes in the [[monoclinic system]].<ref>{{cite journal|title=Verfeinerung der Struktur von Azurit, Cu<sub>3</sub>(OH)<sub>2</sub>(CO<sub>3</sub>)<sub>2</sub>, durch Neutronenbeugung|author1=Zigan, F.|author2=Schuster, H.D.|journal=Zeitschrift für Kristallographie, Kristallgeometrie, Kristallphysik, Kristallchemie|year=1972|volume=135|issue=5–6|pages=416–436|doi=10.1524/zkri.1972.135.5-6.416|bibcode=1972ZK....135..416Z|s2cid=95738208 }}</ref> Large crystals are dark blue, often prismatic.<ref name=Mindat/><ref name=Webmin/><ref name="HurlbutKlein"/> Azurite specimens can be massive to nodular or can occur as [[Druse (geology)|drusy]] crystals lining a cavity.<ref name=Sinkankas>{{cite book |last1=Sinkankas |first1=John |title=Mineralogy for amateurs. |date=1964 |publisher=Van Nostrand |location=Princeton, N.J. |isbn=0442276249 |pages=379–381}}</ref>

Azurite has a [[Mohs hardness]] of 3.5 to 4. The [[specific gravity]] of azurite is 3.7 to 3.9. Characteristic of a carbonate, specimens effervesce upon treatment with hydrochloric acid. The combination of deep blue color and effervescence when moistened with hydrochloric acid are identifying characteristics of the mineral.<ref name="HurlbutKlein"/><ref name=Sinkankas/>

===Color===
The optical properties (color, intensity) of minerals such as azurite and malachite are characteristic of copper(II). Many [[Coordination complex#Color|coordination complexes]] of copper(II) exhibit similar colors. According to [[crystal field theory]], the color results from low energy d-d transitions associated with the d<sup>9</sup> metal center.<ref>{{cite journal |last1=Nassau |first1=K. |year=1978 |title=The origins of color in minerals |journal=American Mineralogist |volume=63 |number=3–4 |pages=219–229}}</ref>{{sfn|Klein|Hurlbut|1993|pp=260-263}}

===Weathering===
Azurite is unstable in open air compared to malachite, and often is [[pseudomorph]]ically replaced by [[malachite]]. This weathering process involves the replacement of some of the carbon dioxide (CO<sub>2</sub>) units with water (H<sub>2</sub>O), changing the carbonate:hydroxide ratio of azurite from 1:1 to the 1:2 ratio of malachite:<ref name=HurlbutKlein/>

: 2 Cu<sub>3</sub>(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>2</sub> + H<sub>2</sub>O → 3 Cu<sub>2</sub>(CO<sub>3</sub>)(OH)<sub>2</sub> + CO<sub>2</sub>

From the above equation, the conversion of azurite into malachite is attributable to the low partial pressure of carbon dioxide in air.

Azurite is quite stable under ordinary storage conditions, so that specimens retain their deep blue color for long periods of time.<ref name=Desautels>{{cite journal |last1=Desautels |first1=Paul E. |title=Some Thoughts about Azurite |journal=Rocks & Minerals |date=January 1991 |volume=66 |issue=1 |pages=14–23 |doi=10.1080/00357529.1991.11761595|bibcode=1991RoMin..66...14D }}</ref>

===Occurrences===
[[File:Azurite, Burra Mine, South Australia.jpg|thumb|Azurite from Burra Mine, South Australia]]
Azurite is found in the same geologic settings as its sister mineral, malachite, though it is usually less abundant. Both minerals occur widely as [[supergene (geology)|supergene]] copper minerals, formed in the [[oxidized]] zone of copper ore deposits. Here they are associated with [[cuprite]], [[native copper]], and various [[iron oxide]] minerals.<ref name=HurlbutKlein/>

Fine specimens can be found at many locations. Among the best specimens are found at [[Bisbee, Arizona]], and nearby locations, and have included clusters of crystals several inches long and spherical aggregates and rosettes up to {{convert|2|in||sp=us}} in diameter. Similar rosettes are found at [[Chessy, Rhône]], France. The best crystals, up to {{convert|10|in||sp=us}} in length, are found at [[Tsumeb]], [[Namibia]]. Other notable occurrences are in [[Utah]]; [[Mexico]]; the [[Ural Mountains|Ural]] and [[Altai Mountains]]; [[Sardinia]]; [[Mines of Laurion|Laurion, Greece]]; [[Wallaroo, South Australia]]; Brazil and [[Broken Hill]].<ref name=Sinkankas/>

==Uses==
===Pigments===
Azurite is unstable in air, however it was used as a [[Azurite (pigment)|blue pigment]] in antiquity.<ref>Gettens, R.J. and Fitzhugh, E.W., "Azurite and Blue Verditer", in ''Artists' Pigments: A Handbook of Their History and Characteristics'', Vol. 2: A. Roy (Ed.) (1993). Oxford University Press. pp. 23–24.</ref> Azurite is naturally occurring in Sinai and the Eastern Desert of Egypt. It was reported by [[Flaxman Charles John Spurrell|F. C. J. Spurrell]] (1895) in the following examples; a shell used as a pallet in a [[Fourth Dynasty of Egypt|Fourth Dynasty]] (2613 to 2494 BCE) context in [[Meidum]], a cloth over the face of a [[Fifth Dynasty of Egypt|Fifth Dynasty]] (2494 to 2345 BCE) mummy also at [[Meidum]] and a number of [[Eighteenth Dynasty of Egypt|Eighteenth Dynasty]] (1543–1292 BCE) wall paintings.<ref>{{Cite book|title=Ancient Egyptian Materials and Technology|last1=Nicholson|first1=Paul|last2=Shaw|first2=Ian|publisher=Cambridge University Press|year=2000|isbn=978-0521452571}}</ref> Depending on the degree of fineness to which it was ground, and its basic content of copper carbonate, it gave a wide range of blues. It has been known as ''mountain blue'', ''Armenian stone'', and ''azurro della Magna'' (''blue from Germany'' in [[Italian language|Italian]]). When mixed with oil it turns slightly green. When mixed with [[egg yolk]] it turns green-grey. It is also known by the names ''[[Bice|blue bice]]'' and ''blue verditer'', though ''[[Copper(II) hydroxide|verditer]]'' usually refers to a pigment made by chemical process. Older examples of azurite pigment may show a more greenish tint due to weathering into malachite. Much azurite was mislabeled ''[[lapis lazuli]]'', a term applied to many blue pigments. As chemical analysis of paintings from the [[Middle Ages]] improves, azurite is being recognized as a major source of the blues used by medieval painters. Lapis lazuli (the pigment ultramarine) was chiefly supplied from Afghanistan during the Middle Ages, whereas azurite was a common mineral in Europe at the time. Sizable deposits were found near Lyons, France. It was mined since the 12th century in [[Saxony]], in the silver mines located there.<ref>Andersen, Frank J. ''Riches of the Earth''. W.H. Smith Publishers, New York, 1981, {{ISBN|0-8317-7739-7}}</ref>

Heating can be used to distinguish azurite from purified natural [[ultramarine]] blue, a more expensive but more stable blue pigment, as described by [[Cennino D'Andrea Cennini]]. Ultramarine withstands heat, whereas azurite converts to black copper oxide.<ref>{{cite journal |last1=Muller |first1=Norman E. |title=Three Methods of Modelling the Virgin's Mantle in Early Itallan Painting |journal=Journal of the American Institute for Conservation |date=January 1978 |volume=17 |issue=2 |pages=10–18 |doi=10.1179/019713678806029166}}</ref> However, gentle heating of azurite produces a deep blue pigment used in Japanese painting techniques.<ref>{{cite journal |last1=Nishio |first1=Yoshiyuki |title=Pigments Used in Japanese Paintings |journal=The Paper Conservator |date=January 1987 |volume=11 |issue=1 |pages=39–45 |doi=10.1080/03094227.1987.9638544}}</ref>

Azurite pigment can be synthesized by precipitating [[copper(II) hydroxide]] from a solution of [[copper(II) chloride]] with [[lime (material)|lime]] ([[calcium hydroxide]]) and treating the precipitate with a concentrated solution of [[potassium carbonate]] and lime. This pigment is likely to contain traces of basic copper(II) chlorides.<ref>{{cite journal |last1=Orna |first1=Mary Virginia |last2=Low |first2=Manfred J. D. |last3=Baer |first3=Norbert S. |title=Synthetic Blue Pigments: Ninth to Sixteenth Centuries. I. Literature |journal=Studies in Conservation |date=May 1980 |volume=25 |issue=2 |pages=53 |doi=10.2307/1505860|jstor=1505860 }}</ref>

<gallery mode="packed" heights="200px">
File:Azuritepigment.jpg|Ground azurite for use as a pigment
File:Lady with a Squirrel.jpg|The background of ''Lady with a Squirrel'' by [[Hans Holbein the Younger]] was painted with azurite
File:Madonna and Child Enthroned with Saints.jpg|The greenish tint of the Madonna's mantle in [[Raphael]]'s ''Madonna and Child Enthroned with Saints'' is due to azurite weathering to malachite
</gallery>

===Jewelry===
Azurite is used occasionally as beads and as [[jewelry]], and also as an ornamental stone.<ref>{{cite journal |last1=Mueller |first1=Wolfgang |title=Arizona Gemstones |journal=Rocks & Minerals |date=31 January 2012 |volume=87 |issue=1 |pages=64–70 |doi=10.1080/00357529.2012.636241  |bibcode=2012RoMin..87...64M |s2cid=219714562 |language=en |issn=0035-7529}}</ref> However, its softness and tendency to lose its deep blue color as it weathers leaves it with fewer uses.<ref>{{cite book |last1=Schumann |first1=Walter |title=Gemstones of the world |date=2009 |publisher=Sterling |location=New York |isbn=9781402768293 |edition=4th, newly rev. & expanded |url=https://books.google.com/books?id=V9PqVxpxeiEC&q=azurite |access-date=18 September 2021}}</ref> Heating destroys azurite easily, so all mounting of azurite specimens must be done at room temperature.

===Collecting===
The intense color of azurite makes it a popular collector's stone. The notion that specimens must be carefully protected from bright light, heat, and open air to retain their intensity of color over time may be an [[urban legend]]. Paul E. Desautels, former curator of gems and minerals at the [[Smithsonian Institution]], has written that azurite is stable under ordinary storage conditions.<ref name=Desautels/>

===Prospecting===
While not a major ore of copper itself, the presence of azurite is a good surface indicator of the presence of weathered [[copper sulfide]] ores. It is usually found in association with the chemically similar malachite, producing a striking color combination of deep blue and bright green that is strongly indicative of the presence of copper ores.<ref name=HurlbutKlein/>

==History==
Azurite was known in the pre-classical [[ancient world]]. It was used in [[ancient Egypt]] as a pigment, obtained from mines in [[Sinai Peninsula|Sinai]]. [[Ancient Mesopotamia]]n writers report the use of a special [[mortar and pestle]] for grinding it. It was also used in ancient [[Greece]], for example on the [[Acropolis]] in Athens. It does not appear to have been used in [[ancient Roman]] wall paintings but Roman writers certainly knew about its use as a pigment.<ref>Robert James Forbes, ''Studies in Ancient Technology'', vol. 1, p. 216, Leiden: E. J. Brill, 1955 {{oclc|312267983}}.</ref> The [[glass fusing|fusing]] of glass and azurite was developed in ancient Mesopotamia.<ref>Emmerich Paszthory, "Electricity generation or magic? The analysis of an unusual group of finds from Mesopotamia", p. 34 in, Stuart J. Fleming, Helen R. Schenck, ''History of Technology: The Role of Metals'', University of Pennsylvania Museum of Archaeology, 1989 {{ISBN|0924171952}}.</ref>

==Gallery==
<gallery widths="125" heights="125" mode="packed">
Azurite from China.jpg|Azurite crystals from China
File:Azurite from Arizona, collected by Dr John Hunter in the 18th century, Hunterian Museum, Glasgow.jpg|Azurite from Arizona, collected by Dr John Hunter in the 18th century, Hunterian Museum, Glasgow
File:Mineraly.sk - azurit.jpg|Fresh, unweathered azurite crystals showing the deep blue of unaltered azurite. From [[Špania Dolina]], [[Slovakia]]
File:Azurite with Malachite - National Museum of Natural History - Washington, D.C..jpg|Azurite with Malachite, Copper Queen mine, [[Bisbee, Arizona]]
File:Azurite-23164.jpg|Azurite from [[Touissit]], Morocco
File:Azurite-284714.jpg|Azurite, [[Morenci, Arizona]]
File:Azurite in siltstone, Malbunka mine NT.jpg|Azurite in [[siltstone]], Malbunka mine, [[Northern Territory]], Australia
File:Azurite-den07-03b.jpg|Azurite from [[Tsumeb]], Namibia
File:Azurite Bisbee ROM.jpg|Azurite, cross-section through merged [[stalactite]]s, [[Bisbee, Arizona]]
File:Batu Azurite.jpg|Azurite from [[Bandung]], Indonesia
File:Sparkly Azurite Crystal 01.jpg|Azurite crystal, from the minerals collection at the [[Natural History Museum, London]].
File:Azurite spheroids.jpg|Spheroidal azurite specimens from [[Utah]]
</gallery>

==See also==
* [[Basic copper carbonate]]
* [[Blue pigments]]
* [[List of inorganic pigments]]
* [[List of minerals]]

==References==
{{Reflist}}

==External links==
{{Commons category|Azurite}}
*{{cite EB1911|wstitle=Azurite |volume=3 |page=86 |first=Leonard James|last=Spencer|author-link=Leonard James Spencer|short=x}}
* [http://colourlex.com/project/azurite/ Azurite], Colourlex

{{Authority control}}

[[Category:Carbonate minerals]]
[[Category:Copper ores]]
[[Category:Gemstones]]
[[Category:Monoclinic minerals]]
[[Category:Minerals in space group 14]]