Editing Azurite (section)

==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/>