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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

MAGNESITE


MAGNESITE (Magnesit—Magnésite—ћагнезит) (Delamétherie, 1797 in Karsten, D.L.G. 1808), from Gk. “magnesio lithos” – magnesian stone, a kind of ore from Magnesio, the coastal district of ancient Thessaly, Greece; or one of two localities in Turkey, now ruins 15 km. of Dilekli (Söke), or modern Dilektaxi (Manis) vilayet.

Composition & Properties. Carbonate – Mg[CO3], trigonal system. Hardness 4-4.5. Density 2.9-3.1. Glass luster, silk one in fibrous aggregates. Cleavage in three directions. Fragile. Magnesite is rarely found as transparent or half-transparent crystals. It is usually found as massive to fine-grained chalky-like or porcelain-like aggregates, which are used as ornamental stones. Not rarely, there are rose-shaped aggregates of spheromagnesite. Color: snow-white with yellowish or grayish tone to lemon and brown. Under weathering, its hydrated solid variety is formed – Bosnian meerschaum, which fills cracks or is represented with stalactites in cavities of dissolution. In serpentinites, there are lemon-yellow nodules nickel magnesite with admixture of gaspeite and chrysoprase – citric chrysoprase. Siliceous magnesite sometimes contains admixtures of opal, which makes it harder. Ferrous magnesite – breunerite contains FeCO3 up to 30%, and nickel magnesite contains NiO up to 4%, and serpentines magnesite, or ophicalcite contains inclusions of serpentine.

Deposits. Magnesite is formed in the process of weathering of basic rocks and also in hydrothermal veins. In Russia, in the South Urals, there are large deposits of magnesite: Satka in the Chelyabinsk Region and Khalilovskoye in the Orenburg Region. At the Satka deposit, they find a special variety of pattern and polychromatic magnesite – caraculiated magnesite with dendrites and spots of manganese oxides. To the south from Miass, at the Kalkanskoye deposit there are ten veins of amorphous magnesite in serpentinites. In the Krasnoyarsk Region ornamental magnesite is known at the Tal’skiy mine, Yeniseiskiy Ridge; in the Rep. of Tyva – at the Ak Dovurak deposit. In Kazakhstan, light green nickel magnesite as veins up to 0.4 cm. thick, sometimes with dendrites of manganese oxides at the Sarykul’boldy chrysoprase deposit, Pribalkhashia, they discovered. In Armenia, ornamental snow-white magnesite at the Shorja deposit, near Dilijhan, is known. In other countries: in Norway – there is the Snarum deposit of magnesite; in Austria – the Radenstein deposits, Carinthia; and Kraubath – in Styria. In Greece, deposits of amorphous magnesite are situated on the Iss. Eubea, Lesbos and on the Kikladhes (Cyclades) Iss. Large blocks of magnesite are extracted in China at the Liaotung deposit, and on the Korean Penin. in the Taikwayodo deposit. In India, transparent magnesite in crystals was found at a deposit near Salem, Tamil Nädu; in Africa – in Congo (Kinshasa) and some other countries. In Central Australia, in weathering crusts on serpentinites they find nodules and veins of gem-quality citric chrysoprase, which is represented with magnesite containing up to 1.6% of nickel. In the U.S.A., deposits of magnesite as veins in serpentinites are in the Border Range, California; in Nevada – in the Clark Co. In Canada, they are situated near Greenville, Québec Prov. In Brazil metacrystals magnesite up to 1 m. in hydrothermal-metasomatic bodies as mell as excellent crystals up to 30 cm in cavities occur at Brumado mine, Bahia. In the same state, at the Pedras Pretas mine, they extract ornamental magnesite.

Synonyms. Breunerite, after the Germ. Count Breuner | Ferromagnesite | Morpholite, after its shape | Pinolite | Roubschite | Brown spar | Magnesite spar | Talc spar.

Cut Gems. Gem-quality magnesite from Brazil is enough good to receive faceted stones up to 10-15 car and even up to 100 car from it; the ones have only collection significance. Ornamental varieties are processed in cabochons and are used in stone-carving.

Similar Gemstones & Imitations. It looks like dolomite and calcite. Porous gem of magnesite content is well colored, that’s why it can be used as an imitation of turquoise and lazurite.

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