Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia



SPHALERITE group (Sphalerit—Sphalérite——фалерит) (Agricola, 1546; in Glocker, E.F. 1848), from Gk. “sphaleros” – mistaken, because the mineral was often taken for galena, but yielded no lead. In Europe it is usually called “blende”, from Germ. “blenden” – to glisten, because of the diamond luster of its edges. Here is also described a hexagonal polymorph modification of sphalerite – wurtzite.

Composition & Properties. Cubic sulfide of non-metallic view – ZnS. Hardness 3.5-4. Density 3.9-4.5. Half-metallic luster to diamond one. High dispersion. Perfect cleavage in six directions. Fragile. Sphalerite is found in the form of isometric crystals, grained masses and cryptocrystalline kidney-shaped aggregates. Non-transparent to translucent, in crystals it can be transparent. Color: black, brown, orange, orange-red, yellow, green, rarely colorless. Colorless white blende, light colored cleiophane and cramerite contain almost no admixtures. Amber-yellow sphalerite – honey blende, orange-red – ruby blende, red – Príbramite with the admixture of cadmium up to 5% or germanium, black – marmatit, or chrystophite with the admixture of Iron up to 8-10%, different tones of green are typical for sphalerites with admixture of cobalt (CO2+). Color can depend also on micro-inclusions of ore minerals: galena, pyrite, chalcopyrite and others. Of gem-quality are mainly bright colored varieties of sphalerite. As an ornamental material the most interesting are light brown and yellowish kidney-shaped cryptocrystalline formations of concentric-lamellar texture – shelly sphalerite and stripped aggregates of grained sphalerite – chipmunkan ore, interstratified with quartz, galena, magnetite or with chalcopyrite.

Deposits. Sphalerite is found mainly at hydrothermal deposits, sometimes in metasomatic rocks or in sedimentary layers. It is widespread and it is extracted at numerous deposits throughout the world as zinc ore. In Russia, in the Pay-Kheu Khrebet, they discovered deposits of cadmium sphalerite in the form of red and lavender-yellow crystals in quartz-carbonate veins. In the Middle Urals, in pegmatites and albite-quartz veins of Izumrudnye Kopi (Emerald Mines) they found brownish to black sphalerite – marmatit in crystals up to 4 cm. In the South Urals, it is known at the Kochkar’ deposit, near Plast town. Large crystals of sphalerite, sometimes even transparent ones, were found at ore deposits of Transbaikalia, including Savinskoye-5 – up to 12 cm., Klichka – up to 15 cm. In the Primorskiy Region they are typical for the Dal’negorskoye deposit (form. Tetyukhe). In Rep. Sakha (Yakutia), at the Lebedinskoye deposit, massive aggregates of sphalerite with admixture of chalcopyrite can be of interest as ornamental material.

In the Western Ukraine, at the Truskavets deposit, they discovered colloidal sphalerite in the form of concentric-lamellar aggregates up to 10 cm. in diameter, which received the local name brunckit. In Kazakhstan, at the Zhezkazgan deposit, they found light colored sphalerite, available for faceting, – cleiophane. Similar sphalerite was at the Kuruksay deposit in the North Tadzhikistan. In the South Tadzhikistan, in the Darväz Ridge, at the Iokunj lead-zinc deposit, they found ovoid aggregates of massive, fine-grained sphalerite of olive-brownish color. In Azerbaijan, at the Dashkesan deposit, the weight of sphalerite crystals reached 16 kg. In Spain, at the Aliva mine, Cantabria Prov., and at the Picos de Europe deposit, Santader Prov., they extract gem-quality cleiophane of golden-yellow and red color up to 15 cm., also banded sphalerite. In Romania, crystals of red-brown sphalerite up to 7 cm. at Baia Sprie, at Cavnic (form. Kapnik), at Hârja, and Sâcâramb deposits, all Transylvania, were found. In Slovakia, at the Banská Štiavnica (form. Selmeczbánya) deposit, they found crystals of transparent cleiophane up to 5 cm. In Poland, stalactites of sphalerite were extracted at the Olkusz and Trzebinia deposits, Wojewodztwo Slaskie (Upper Silesia); and in Serbia – at the Trepça deposit. In alpine veins of Austrian Zillertal, at the Lukmanier deposit, Tyrol, they find crystals of sphalerite from colorless to black color, up to 3 cm. in size. In Great Britain, black marmatit was extracted at several deposits. in Cumbria – at Alston Moor; in Cornwall – in the region of Saint Agnes; in Scotland – at Wonlokhid. In Czech Rep., at the Príbram deposit, they discovered red sphalerite, available for processing – príbramite. Massive kidneys of shelly blende and wandering aggregates, available for processing as an ornamental stone, are extracted in Belgium, at a deposit by Liége. Findings of separate transparent crystals of sphalerite were described at deposits of France and Germany, too. In Africa, we should mention Namibia, where the Tsumeb deposit is with crystals of sphalerite, available for faceting, and massive aggregates, which display triboluminescence, when under strike sparkling is observed. In Australia, at the Broken Hill deposit in New South Wales, they find large crystals of sphalerite from dark brown to black color. In China, splendid red transparent crystals occurs at the Taolin and Kangjiawan mines, Hunan Prov. Ani mine, Akita Pref.

In the U.S.A., at the Franklin deposit, New Jersey, they discovered transparent, colorless to pale green cleiophane with segments, available for faceting, up to 3 cm; and in Ohio, at the Tiffin deposit – red príbramite up to 10 cm. Gem-quality sphalerite in crystals up to 20 cm. was found in Missouri – at the Joplin deposit, Jasper Co.; in Montana – at the Butte deposit; in Utah – at Bingham; and other states. In the Illinois, in karst cavities, sphalerite stalactites up to 15 cm. at Galena, Jo Daviess Co., are found. Findings of sphalerite, available for faceting, are known in the neighboring Canada, in Québec, at the Mont St.-Hilaire in crystals up to 7 cm., and in the Ontario Prov., at the Viarton deposit, Bruce Co. In Mexico, in porphyre copper ores, green and red crystals up to 10 cm. were extracted at the Cananea deposits, and Chivor, Sonora; and in the ore region Santa Eulalia, Chihuahua.

Synonyms. Black blende | Garnet blende, after its color | Zinc blende, after the composition, discr. by IMA. | Cleiophane, from Gk. “kleos” – glass and “phanos” – to seem, because of its transparency, syn. rosin jack (resin jack) | Cramerite, after the discovery location near Cramer, at the Backer deposit in California, the U.S.A. | Black jack | Marmatit (marmalite), after the discovery location near Marmato, Cauca Dept. Colombia | Nuttal, colorless, obs. | Príbramite, after the Príbram deposit, Czech Rep. | Pseudogalena | Rahtite, after Amer. researcher Raht | Ruby zinc.

Cut Gems. Bright colored crystals of sphalerite are often processed because of their strong diamond luster and the effect of fire in faceted stones. Their weight is usually not more than 40 ct., and at the same time the perfect cleavage in six directions makes the processing very difficult. Because of its low hardness, sphalerite is mainly of collection importance. Massive varieties are cut in cabochon. Large faceted stones usually are with defects in the form of inclusions, veils and cracks. Reddish sphalerites from Spain reach 100 ct. in the faceted form and in cabochons. In the U.S.A., there were found a stone in 133.4 ct. in Utah; in Mexico – in 50 ct. In the Smiths. Inst., Wash., there are several faceted sphalerites: a brownish-yellow one from Utah – 73.3 ct., a yellowish-green cleiophane from New Jersey –– 59.5 ct., a yellow one from Mexico – 48 ct., a yellow one from Spain – 45.9 ct.

Synthesis. In jewelry work of art, as material for faceting, they sometimes use synthetic sphalerite, which can be manufactured of different colors: green, canary-yellow and colorless. Besides, they use synthetic zinc selenide – ZnSe with the density 5.42 for the same purpose.

Similar Gemstones. Sphalerite looks like many other yellow gemstones, including garnets, cassiterite, zircon, and colorless one looks like diamond.

Wurtzite (Wurtzit—Wurtzite—¬юртцит) (Friedel, C. 1861), after Fr. chemist Charles Adolphe Wurtz (1817-1884). Sulfide – ZnS, hexagonal system. Hardness 3.5-4. Density 4-4.5. Galls luster to diamond one according the cleavage planes. Cleavage in two directions. Fragile. Wurtzite, or radial zinc blende, is polymorph with sphalerite. Its pyramidal crystals are usually not more than 2 cm. long, but more often it is found in the form of radial, fibrous and cryptocrystalline aggregates. For schalenblende it is typical to form cryptocrystalline concentric-zonal aggregates up to 10 cm. Color: from light yellow to dark brown, for varieties enriched with Iron – red-brown to black; for varieties enriched with the admixture of cadmium— orange, green and brownish. It looks like hübnerite. As a gemstone, it is of no practical interest. In Russia its large crystals up to 3 cm. were found at the Talnakh deposit, Krasnoyarsk Region. In the Ukraine, in the Zakarpats’ka Region, near Berehove, radial-rayed aggregates of wurtzite reached the size of 6 cm. In Bolivia, it is known at the deposits Llallagua and Animas, Potosí Dept. with fine crystals up to 4 cm.

Synonyms. Bergerite | Spiauterit, obs.

Synthesis. For jewelry purposes they use synthtetic wurtzite, which is manufactured of different colors – green, yellow or colorless.