Locations for Dioptase

Dioptase is formed as a supergene mineral in the oxide zones of deeply weathered copper sulfide deposits. Typical common copper sulfides are chalcopyrite, chalcocite, covellite, and bornite. Dioptase grows from leachant solutions produced by these weathering sulfides that are rich in copper ions and solvated silicate, the solubility of the latter being proportional to pH. Therefore the conditions under which dioptase forms requires neutral to alkaline pH. Natural buffering of the inherently acidic leachant copper ion-rich solutions must be present. Typically, the buffering agent is carbonate as calcite in limestones. The carbonate in the calcite neutralizes the acid to form carbon dioxide and water. This is why crystals of calcite or other carbonate minerals are so often found with dioptase, examples of which are the dioptases from the type locality of Altyn Tyube, Kazakhstan and those from Tsumeb, Namibia- the former most often occurring on beds of white calcites and the latter being associated with many carbonates such as calcite, dolomite, and smithsonite. Other copper silicates such as chrysocolla, plancheite, and shattuckite are often associated with dioptase. Specimens from various specimen mines on the Kaokoveld Plateau of Namibia had sufficient pH buffering during their formation to exhibit an interesting and diverse paragenesis of copper silicates. Dioptase specimens from here can be observed associated with sky blue, fuzzy botryoidal shattuckite and plancheite, as well as resinous chrysocolla, all which are copper silicates. Excellent sprays and large crystals of malachite are also commonly found here with the dioptase.

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Dioptase can also be found with other secondary minerals formed by weathering metal sulfides. The best examples of these are from Tsumeb, Namibia and Tiger, Arizona. The Tsumeb, Namibia specimens are associated with willemite, cerussite, mottramite, heterogenite, duftite, and scores of other metal-containing secondaries. These feature extremely large and clear crystals and are the finest of the species. Specimens of dioptase from Tiger, Arizona are small but very euhedral and bright, ofen occuring in spherical aggregates with or coatings covering thin, bright orange wulfenite blades. This is a classic association rarely found elsewhere worldwide. Specimens of this combination are very valuable.

Dioptase

Dioptase from the Tantara mine in the DRC can be found pseudomorphing calcite. This is very rare and occurs as calcite redissolves with decreasing pH, pushing copper silicate out of solution as dioptase which nucleates on similarly structured trigonal calcite and replaces it. This find produced many fine clusters often on a matrix of solid massive dioptase.

Kimbedi in the Republic of the Congo may be the producer of the largest crystals of dioptase which reach around 3cm. A find in 2011 released many fine large cabinet plates of dioptase to the public market. They are very similar to the specimens from the Tantara mine and are covered in large semitransparent deep emerald green crystals.

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