Deposits of Chromite in California, Oregon, Washington, and Montana (Department of the Interior, United States Geological Survey, Bulletin 725-A)

84 pp. Includes black-and-white plates and illustrations. Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite (MgCr2O4). A substitution of the element aluminium can also occur, leading to hercynite (FeAl2O4). Chromite today is mined particularly to make stainless steel through the production of ferrochrome (FeCr), which is an iron-chromium alloy. Chromite is iron-black in color with a metallic luster, a dark brown streak and a hardness on the Mohs scale of 5.5.