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Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia

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DIOPTASE


DIOPTASE (Dioptas—Dioptase—ƒиоптаз) (Haüy, R.-J. 1797), from Gk. “dia” – through and “optasia” – vision, because its cleavage planes may be seen on looking into the transparent crystal.

Composition & Properties. Silicate – Cu6[Si6O18]·6H2O, subclasses ring silicate. Trigonal system. Hardness 5. Density 3.3. Glass luster. Perfect cleavage in three directions. Fragile. Dioptase is a rare gemstone, mainly of collection interest. It was discovered in Kazakhstan, near Altyn Tyube by Aschir Akhmed, a merchant from Bukhara, in 1785, and sent to the Russian Academy of Science, where it was called at first aschirite. It is found in the form of short-columnar to oblong crystals, which form druses, and in columnar and fine grained aggregates to complete joint masses. Transparent to translucent. Color: light bluish-green to emerald-green, that’s why it was also called copper emerald. Dioptase is partly replaced with planchéite and chrysocolla.

Deposits. Dioptase is formed in zones of oxidation of copper-sulfide ore deposits. In Russia, in the Krasnoyarsk Region, in the Yenisey Ridge, dioptase is found in small quantities in the basin of the Tarada River, where its crystals were found in parallel-columnar aggregates together with chrysocolla. In the Irkutsk Region, it was discovered in the basin of the Angara River; in the Khabarovsk Region – at the Khinganskoye sulfide-cassiterite deposit. In Central Kazakhstan, to the east from Karaganda, dioptase in crystals up to 5 cm. and in its druses is extracted at the Altyn Tyube deposit, which has been known for more than 200 years. In Iran, dioptase is discovered in the Anaräk area, at the Sebarz lead-zinc deposit, as well as at deposits of the area of ‘Abdoläbäd and Näïgün. In Israel, it was discovered in Negev Desert at the Timna deposit. In Europe, dioptase was described at first in Romania, at the B˘ ai¸ ta Bihor deposit, near Rezbanja, where they found small quantities of gem-quality material. In Italy, dioptase is known on the Elba Is., at the Capo Calamita mine. In Congo (Kinshasa, form. Zaire), there are deposits of dioptase Mashamba and Kolwezi, Sheba Prov. In Congo (Brazzaville), there are similar deposits in the Niari Valley, near Renéville. There, at the deposits Minduli and M’Fuati, they find separate well-formed crystals of dioptase up to 3 cm., which are called emeraudine, and their accumulations up to 70 cm. in size. In Congo, therefore, dioptase was a national symbol of country. In Namibia, dioptase is found at the deposits Tsumeb and Guchab, Otavi Mts., also at Kaokoveld deposit in the form of perfect crystals up to 5 cm. Besides, large crystals of dioptase were discovered in Angola, at the Mavoio deposit. In the U.S.A., deposits of dioptase are known in Arizona – at the deposits Mammoth, Tiger Co.; in California – in Blue Bell, San Bernardino Co.; and in the New York State – in the St Lawrence Co. In Chile, dioptase was discovered near Copiapó, Atacama region; in the Argentina as druses of crystals up to 2 cm. in the Malpaso quarry and at Chiviquin, Cordoba Prov.

Synonyms. Aschirite (achirite), after the name of the merchant Aschir, who discovered this mineral | Chrysocolla chert | ~ Emerald: Congo ~, copper-siliceous ~, Kirghiz ~, malachite ~ | Emerandine, obs. | Emerauldine, obs. | Kirghisite, obs. | Pseudoemerald | Scheibeliite, obs. | Malachite-smaragd | Smaragdochalcit.

Treatment. Dioptase has been known since the antiquity, when Pliny the Elder described it on the Cyprus Is. as pseudoemerald. In Kazakhstan, the most ancient extraction of dioptase at the Altyn Tyube deposit are dated to 700-500 B.C. Because of its perfect cleavage dioptase is difficult in faceting. Only tips of crystals are available for it. Faceted stones are made mainly for collection purposes; they are not more than 2 ct. It is also cut in cabochons, which are sometimes more than 15 ct. Crusts of small crystals are used as insets in rings and brooches. In the Museum of Ottawa, Canada, there is a faceted stone from Namibia 0.63 ct.

Similarity. Dioptase looks like demantoid, diopside, emerald, uvarovite, and fluorite.

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