Dioptase
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Melesse
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{{Infobox mineral
| name = Dioptase
| category =
| boxwidth =
| boxbgcolor =
| image = Dioptase Kazakhstan.jpg
| caption = Dioptase from Kazakhstan
| formula = [[Copper]] [[silicate]] hydrate: CuSiO<sub>3</sub>'''·'''H<sub>2</sub>O
| molweight =
| color = Dark blue green, emerald green
| habit = Six sided prisms terminated by rhombohedrons to massive
| system = [[Trigonal]]; bar 3
| twinning =
| cleavage = Perfect in three directions
| fracture = Conchoidal and brittle
| mohs = 5
| luster = Vitreous
| refractive = 1.65–1.71
| opticalprop =
| birefringence =
| pleochroism =
| streak = Green
| gravity = 3.28–3.35
| melt =
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}}
'''Dioptase''' is an intense [[emerald (color)|emerald]]-green to bluish-green [[copper]] [[silicate minerals|cyclosilicate]] [[mineral]]. It is transparent to [[translucent]]. Its [[lustre (mineralogy)|luster]] is [[vitreous]] to sub-[[adamantine]]. Its formula is CuSiO<sub>3</sub>'''·'''H<sub>2</sub>O (also reported as CuSiO<sub>2</sub>(OH)<sub>2</sub>). It has a [[hardness]] of 5, the same as tooth enamel. It [[specific gravity]] is 3.28–3.35, and it has two perfect and one very good [[cleavage (crystal)|cleavage]] directions. Additionally, dioptase is very fragile and specimens must be handled with great care. It is a [[trigonal]] mineral, forming 6-sided [[crystal]]s that are terminated by rhombohedra.
==History==
Late in the 18th century, copper miners in [[Kazakhstan]] thought they found an [[emerald]] deposit of their dreams. They found fantastic cavities in [[quartz]] veins in a [[limestone]], filled with thousands of lustrous emerald-green transparent crystals. The crystals were dispatched to [[Moscow]], [[Russia]] for analysis. However the mineral's inferior hardness of 5 compared with emerald's greater hardness of 8 easily distinguished it. Later Fr. [[René Just Haüy]] (the famed French [[mineralogist]]) in [[1797]] determined that the enigmatic Kazakhstani mineral was new to science and named it dioptase ([[Greek language|Greek]], ''dia'', "through" and ''optima'', "vision"), alluding to the mineral's two cleavage directions that are visible inside unbroken crystals.
==Occurrence==
[[Image:Dioptase in Matrix from Namibia.jpg|thumb|250px|left|Dioptase in [[calcite]] matrix, from the Tsumeb Mine, [[Tsumeb]], [[Namibia]].]]
Dioptase is a very rare mineral found mostly in [[desert]] regions where it forms as a secondary mineral in the [[oxidation|oxidized]] zone of copper [[sulfide]] mineral deposits. However, the process of its formation is not simple, the [[oxidation]] of copper sulfides should be insufficient to crystallize dioptase as [[silica]] is normally minutely soluble in water except at highly [[alkaline]] [[pH]]. The oxidation of sulfides will generate highly [[acidic]] fluids rich in [[sulfuric acid]] that should suppress silica solubility. However, in dry climates and with enough time, especially in areas of a mineral deposit where acids are [[buffering agent|buffer]]ed by [[carbonate]], minute quantities of silica may react with dissolved copper forming dioptase and [[chrysocolla]].
The Altyn Tube mine still provides handsome specimens, a brownish quartzite host distinguishes its specimens from other localities. The finest specimens of all were found at the now-shut Tsumeb Mine in [[Tsumeb]], [[Namibia]]. Tsumeb dioptase is wonderfully lustrous and transparent, with its crystal often perched on an attractive snow-white carbonate matrix. Dioptase is also found in the deserts of the southwestern [[USA]]. A notable occurrence is the Mammoth-Saint Anthony Mine in Tiger, [[Arizona]] where small crystals that make fine [[micromount]] specimens are found. In addition, many small, pale-green colored crystals of dioptase have come from the Christmas Mine near [[Hayden, Arizona]]. Finally, an interesting occurrence is the Malpaso Quarry in [[Argentina]]. Here tiny bluish-green dioptase is found on and in [[quartz]]. It appears at this occurrence, dioptase is primary and has crystallized with quartz, native copper, and [[malachite]].
[[Image:dioptase09.jpg|thumb|right|250px|Green crystals of the secondary copper mineral dioptase]]
==Use==
Dioptase is popular with mineral collectors and it is occasionally cut into small emerald-like [[gemstone|gem]]s. Dioptase and [[chrysocolla]] are the only relatively common copper silicate minerals. A rare dioptase gem should never be exposed to [[ultrasonic]] cleaning or the fragile gem will shatter.
==References and external links==
{{commonscat|Dioptase}}
* Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., ISBN 0-471-80580-7
* [http://mineral.galleries.com/minerals/silicate/dioptase/dioptase.htm Mineral Galleries]
* [http://webmineral.com/data/Dioptase.shtml Webmineral]
* [http://mindat.org/min-1295.html Mindat.org]
* [http://mineralgallery.co.za/dioptase.htm Mineral Gallery]
==See also==
*[[aventurine]]
*[[malachite]]
[[Category:Gemstones]]
[[Category:Copper minerals]]
[[Category:Silicate minerals]]
[[de:Dioptas]]
[[es:Dioptasa]]
[[fr:Dioptase]]
[[hr:Dioptas]]
[[it:Dioptasio]]
[[nl:Dioptaas]]
[[pl:Dioptaz]]
[[ru:Диоптаз]]
[[sk:Dioptas]]
[[fi:Dioptaasi]]