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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

PROUSTITE


PROUSTITE (Proustit—Proustite—ѕрустит), named after J.L. Proust (1755-1826), Fr. chemist (Beudant, F.S. 1832). On his opinion, the mineral was known to Agricola in 1546.

Composition & Properties. Sulfosalt – Ag3[AsS3], trigonal system. Hardness 2.5. Density 5.6. Diamond luster. Cleavage in one direction. Fragile. Proustite is found in the form of columnar crystals of typical gemimorphous shape or in grained masses. Not rarely, its crystals form twin clusters. Translucent to transparent. Color bright red. It displays strong pleochroism in red tones. It forms a row of constant miscibility with pyrargyrite.

Deposits. Proustite is formed in ore veins of silver-lead-zinc formation, and alas well as a secondary mineral of the oxidation zone of these deposits. In Russia, gem-quality crystals of proustite were found at many deposits. In the South Urals, they were found at the Gaiskoye copper deposit; in Sakha (Yakutia) – at the Bezymyannoye deposit, in the region of Verkhoyansk. In North Kazakhstan, they were extracted at the Sarbaiskiy and Sokolovskiy mines, near Kustanai. In other countries, gem-quality crystals of proustite are known in Czech Rep. – in Jáchymov, up to 14.5 cm. in size, and at the Príbram mine – up to 5 cm.; in Romania – at the Rosia Montane deposit. In Germany, this mineral was discovered at the St Andreasberg deposit, in Harz; in the Erzgebirge Mts. – in the region of Freiberg; and also at some deposits of Saxony – Schneeberg, Schlema and others, where they found the biggest crystals of proustite – up to 25 cm. long. Its findings were also registered in France – at the Sainte-Marie aux Mines, Alsace; and in Italy – on the Sardinia Is. In Canada, proustite is extracted at the Cobalt mine, Ontario Prov. In the U.S.A., at the Poorman mine in Idaho, they extracted a block of grained proustite, 225 kg. in 1867. In Mexico, richly faceted crystals of proustite up to 4 cm. were found at the Batopilas deposit, Chihuahua. In Chile, the same size crystals proustite at the Santa Rose mine was found; and in the desert of Atacama they found a crystal, 8.3x4.5x3.5 cm. in size. At the mines Dolores and Chañarcillo, Atacama region, dark red crystals of proustite, up to 15 cm. long to extract. In 1982, they were known under the trade name sanguinite. One of them is kept in the collection of the British Museum, London. At this deposit they found also orange-yellow and cinnabar-red varieties of proustite, so called xanthoconite.

Synonyms. ~ blende: ruby ~, orthorhombic ruby ~, silver ~, arsenical silver ~| Red arsenic ore | Red silver ore | Light-red silver ore | Ruby silver ore | Sanguinite, from Lat. “sanguis” – blood | Red silver | Arsenical red silver | Ruby silver.

Cut Gems. In jewelry they use cabochons of light-red silver ore. When faceted, proustite displays bright color and diamond luster, but because of its low hardness it is of collection interest only. In the British Museum, London, there is a faceted proustite from Germany in 9.9 ct.

Synthesis. Synthetic proustite was produced in 1977 with the method of directed crystallization in the bull form up to 4x8 cm. It can be used for jewelry purposes.

Similarity. Proustite looks like cinnabar, cuprite, pyrargyrite and zincite.

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