Element Tungsten, W, Transition Metal
|Tungsten was produced by de Elhuyar brothers, students of Bergman in 1783. They named the new metal wolfram, after the mineral wolframite in which tungsten oxide was found. Miners of 1416 centuries noticed that roasting of the ore tales the tin away, transferring it into slag. They called the ore "wolf's froth" which then was converted into wolfram. Agricola in 1546 named it as Lupi spuma, which meant wolf's foam; in German "wolf rahm". Miners said about tungsten that it "eats" tin as a wolf eats sheep. In 1781 Karl Wilhelm Scheele analyzed white mineral, named tungsten later named scheelite, CaWO4, the name of element which has been accepted I English.|
|Tungsten usually occurs in nature as tungstates of iron, manganese, and calcium. The most important mineral is wolframite, which consists essentially of an isomorphous mixture of iron and manganese tungstates, (FeMn)WO4. It is found in the Urals, Spain, Saxony, New England, Colorado, New South Wales, Malaya, and in Cumberland and Cornwall, usually in massive or platy aggregates of a black or brownish-black colour; sometimes in well-formed monoclinic crystals. The ore possesses one very perfect cleavage which causes it to split readily into thin flakes; it has density about 7.3 and hardness 5.5. It usually accompanies tin ores, from which it may be separated by electro-magnetic methods. The proportions of iron and manganese present vary within wide limits, but usually Fe:Mn = 4:1 or 2:3. The most usual composition of wolframite is FeO = 18.96 per cent.; MnO = 4.67 per cent.; WO3 = 76.37 per cent. Minerals containing more than 80 per cent. MnWO4 are known as hubnerite, and such are found in Nevada and South Dakota. Ferberite was the name given to massive granular crystals of wolframite found with quartz in Southern Spain and believed to be pure ferrous tungstate, FeWO4, a conclusion which was not borne out by analysis. However, specimens from South Dakota have been shown to contain no manganese. Ferrous tungstate also occurs as reinite, in Japan, in the form of tetragonal pyramids. |
Ferritungstite, Fe2O3.WO3.6H2O, occurs associated with quartz in the State of Washington. It is a brownish-yellow mineral which under the microscope is seen to consist of hexagonal plates.
Scheelite, which is usually associated with crystalline rocks, is tetragonal calcium tungstate, CaWO4, of density 6.00 and hardness 4 to 5. It is very widely distributed and usually, though not invariably, contains some molybdenum. In Perak and Selangor fluorspar is usually found with it. It usually occurs in the massive form, generally of a yellow or pale brown colour, but sometimes reddish and possessing a curious waxy lustre.
Tungstite, or tungsten ochre, of which the colour varies from bright yellow to a greenish shade, occurs with wolframite in Cumberland and in Cornwall. It is essentially anhydrous tungsten trioxide, WO3, though hydrated forms have been found. That described by Carnot was said to correspond to the formula WO3.2H2O, and was called meymacite, while more recently a tungstite, of density 5.52, apparently WO3.H2O, has been found in veins of gold quartz in British Columbia.
Other minerals containing tungsten are rare - stolzite, of density 8.00, from Bohemia, Chili, and Massachusetts, is tetragonal lead tungstate, PbWO4; in the monoclinic form lead tungstate occurs as raspite; chillagite, a mixture of lead tungstate and lead molybdate, is found in Queensland; cuproscheelite or cuprotungstite, (CaCu)WO4, is obtained from Chilian copper mines. Tungstenite, a mineral analogous to molybdenite, occurs in Utah. It is essentially the sulphide WS2 (about 61 per cent.) and resembles graphite in appearance. It has density 7.4 and is soft enough to mark paper.
Tungsten occurs mostly as complex oxidized compounds composed by WO3 and iron or manganese, calcium, copper, lead, thorium and, sometimes, rare earth elements oxides. Wolframite is the most abundant mineral. It is a solid solution of iron and manganese tungstates (wolframates) mFeWO4.xnMnWO4 which are salts of tungstic (wolframic) acid. Tungsten ores are associated with granites. Mai deposits are located in China, Myanmar, USA, Bolivia and Portugal, as well as in Ural, Caucasus and Transbaikalia regions of Russia.
Large wolframite and scheelite crystals are very rare. Usually they are found only as inclusions in granites with the average tungsten concentration around 1...2%.