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Wolframite

WOLFRAMITE, or WOLFRAM, a mineral consisting of ironmanganese tungstate, (Fe, MnJWO^ The name is of doubtful origin, but it has been assumed that it is derived from the German Wolf and Rakm (froth), corresponding with the spuma lupi of old writers, a term hardly appropriate, however, to the mineral in question. Wolframite crystallizes in the monoclinic system, with approximation to an orthorhombic type; and the crystals offer perfect pinacoidal cleavage. The colour of wolframite is generally dark brownish-black, the lustre metallic or adamantine, the hardness 5 to 5-5, and the specific gravity 7-1 to 7-5. Wolframite may be regarded as an isomorphous mixture, in variable ratio, of iron and manganese tuugstates, sometimes with a small proportion of niobic and tantalic acids. It was in wolframite that the metal tungsten was first recognized in 1785 by two brothers, J. J. and F. d'Elhuyar. At the present time the mineral is used in the manufacture of tungsten-steel and in the preparation of certain tungstates.

Wolframite is commonly associated with tin-ores, as in many parts of Cornwall, Saxony and Bohemia. In consequence of the two minerals, cassiterite and wolframite, having nearly the same density, their separation becomes difficult by the ordinary processes of oredressing, but may be effected by means of magnetic separators, the wolframite being attracted by powerful magnets. A process introduced many years ago by R. Oxland consisted in roasting the mixed ore with carbonate of soda, when the wolfram was converted into sodium tungstate, which was easily removed as a soluble salt. Wolframite occurs at many localities in the United States, notably at Trumbull, Conn., where it has been mined, and at Monroe, Conn., where it accompanies bismuth ores. Other localities are in Mecklenburg county, N.C., and in the Mammoth mining district, Nevada. Wolframite has in some cases resulted from the alteration of scheelite, though on the contrary pseudomorphs are known in which scheelite has taken the form ol wolframite. By oxidation wolframite may become encrusted with tungstic ochre, or tungstite, sometimes known as wolframine, a name to be carefully distinguished from wolframite.

As the relative proportions of iron and manganese vary in wolframite, the composition tends towards that of other minerals. Thus there is a manganous tungstate (MnWO) known as hubnerite, a name given by E. N. Riotte, in 1865, in compliment to Adolph Httbner, a Saxon mineralogist. There is also a mineral which contains little more than ferrous tungstate (FeWOO, and is known as ferberite, having been named by A. Breithaupt in 1863 after Rudolph Ferber. The original hubnerite came from the Mammoth district, Nevada, and the ferberite from the Sierra Almagrera in Spain. It is possible that such minerals may represent the extreme terms in the series formed by the varieties of wolframite.

(F. W. R.*)

Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)

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