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Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

DIASPORE


DIASPORE (Diaspor—Diaspore—ƒиаспор) (Haüy R.-J. 1801), from Gk. “diaspherein” – to scatter, alluding to its usual decrepitating when strongly annealed.

Composition & Properties. Hydroxide – α-AlOOH, rhombic system. Hardness 6.5-7. Density 3.4. Glass luster, nacre one on the cleavage planes. Perfect cleavage in two directions. Very fragile. Diaspore is a relatively rare gemstone, which is found in the shape of thick-table and columnar crystals, as well as in flaky and fine-fibrous aggregates of nemalite and cryptocrystalline kidney-shaped formations. The biggest size of its crystals is 30x40 cm. Transparent to translucent. Color: colorless, white, yellowish-brownish to brown – because of the admixture of iron, rose to dark red – because of the admixture of Mn2O3 up to 5%; green – because of chromium (Cr3+). In manganese-containing varieties there is strong pleochroism from violet-blue to pale green to rosy and dark red. In greenish-brown diaspore the admixture of chromium up to 5-6% leads to the alexandrite effect – in the artificial light it becomes reddish-violet. In cabochons from fine-fibrous aggregates of nemalite they observe sometimes the effect of cat’s-eye. Diaspore is rarely faceted: with the diamond, emerald and square patterns. Massive varieties are cut in cabochon. Diaspore looks like gibbsite and corundum.

Deposits. Diaspore is formed in the process of contact metamorphism and metasomatism, in hydrothermal veins and in weathering crust. First of all, diaspore was discovered in samples from Russia, from the Middle Urals, where it was found by the village of Kosoy Brod, near Yekaterinburg. It has been called ferrous kyanite for long. Later, in the same region, it was found in the form of filling the cracks in corundum rock near Sysert’, as well as near the village of Mramorskoye – in the shape of prismatic and board crystals of rose color up to 3 cm. long. In the South Urals, it was found in the Vishnevye Mts., and at the Kyzyl Tash mine, near Kasli, where large rose crystals of diaspore replaced corundum in pockets. At the Sarany deposit in the Perm’ Region, flattened, palm-sized crystals of diaspore with gem-quality sections were discovered in alpine veins. They found also transparent crystals of chrome-diaspore – saranite there, 1.5x1x0.5 cm. in size. In Yakutia, diaspore was discovered at the Chainyt deposit of corundum near Zolotinka on Aldan, where there are perspectives of finding of its gem-quality varieties. In Kazakhstan, gem-quality diaspore was registered at the Kayrakty deposit; in Uzbekistan – at the Ak-Tash deposit; in Azerbaijan – at the Chirgidzor deposit. In F.Y.R.O. Macedonia diaspore available for faceting was found in crystals up to 5x3x1 cm. in size at the Sivech mine, near Prilep. In Slovakia, at the Belá deposit, it is represented with fine-grained variety of rose color. There were findings of transparent crystals of diaspore at deposits of Hungary. In Turkey, occur the best is pale yellow to pale green and light greenish-brown diaspore up to 12 cm. at the Milas deposit, Mugla vilayet.; and the Selçuk deposit, Izmir vilayet. In this region its transparent crystals reach 12 cm. long, and they can make faceted stones up to 10 ct. from them. In cabochons they display the effect of cat’s-eye sometimes. In West Anatolia, crystals up to 5 cm. at the Gümüšh Dag deposit, near Izmir; was extracted. Separate gems from Turkey were 26.97 and even 157.66 ct. In South Africa, diaspore crystals up to 4 cm. occur at the Wessels mine, Northern Cape Prov.; and at deposit near Postmasburg, they described findings of mangan-diaspor up to 7.4 cm. in cross-section. On Madagascar, diaspore was extracted in the form of polychromatic crystals. In China, its crystals were found at the Peitsintsu deposit, Liaoning Prov. In the U.S.A., transparent crystals of diaspore up to 5 cm., from colorless to red-brown in color, at the Chester deposit, Massachusetts; and in Pennsylvania – at Corundum Hill, were discovered.

Synonyms. Empholite, the local name after the deposit in the region of Värmland, Sweden | Medamaite (medamit) | Tanatarite (tantarite), after the Russ. petrologist I.I. Tanatar.

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