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CHROMITE , a member of the See also: spinel See also: group of minerals; an See also: oxide of chromium and ferrous iron, FeCr2O4
.
It is also known as chromic iron or as chrome-iron-ore, and is the chief commercial source of chromium and its compounds
.
It crystallizes in See also: regular octahedra, but is usually found as grains or as granular to compact masses
.
In its iron-black colour with submetallic lustre and See also: absence of cleavage it resembles See also: magnetite (magnetic iron-ore) in appearance, but differs from this in being only slightly if at all magnetic and in the See also: brown colour of its powder
.
The hardness is 51; specific gravity 4.5
.
The theoretical
See also: formula FeCr2O4 corresponds with chromic oxide (Cr203) 68%, and ferrous oxide 32%; the ferrous oxide is, however, usually partly replaced by See also: magnesia, and the chromic oxide by alumina and ferric oxide, so that there may be a gradual passage to picotite or chromespinel
.
Much of the material See also: mined as ore does not contain more than 40 to 50% of chromic oxide
.
In the See also: form of isolated grains the See also: mineral is a characteristic constituent of ultrabasic igneous rocks, namely the peridotites and the serpentines which have resulted from their alteration
.
It is also found under similar conditions in meteoric stones and irons
.
Often these rocks enclose large segregated masses of granular chromite
.
The earliest worked deposits were those in the See also: serpentine of the See also: Bare Hills near Baltimore, See also: Maryland, U.S.A.; it was also formerly extensively mined in See also: Lancaster county, Pennsylvania, and is now mined in California, as well as in See also: Turkey, the Urals, Dun See also: Mountain near Nelson in New Zealand, and Unst in the Shetlands
.
Chrome-iron-ore is largely used in the preparation of chromium compounds for use as pigments (chrome-yellow, &c.) and in See also: calico-printing; it is also used in the manufacture of chrome-See also: steel
.
(L . J . |
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