Chromite, as is indicated by its early crystallization is resistant to the altering affects of high temperatures and pressures. Thus it is capable of going through the metamorphic processes unscathed, while other minerals around it are being altered to serpenti, biotite and garnets. This characteristic also explains chromites use as a refractory component in the bricks and linings of blast furnaces.
Usually magnesium is present in chromite substituting for the iron and in fact a solid solution series exists between chromite and the much rarer mineral magnesiochromite. All chromite specimens in nature contain some magnesium; likewise all natural magnesiochromites contain some iron. Magnesiochromite is grayer in color and in streak and has a slightly lower density than chromite at a specific gravity of 4.2 to 4.4.
Characteristics of Chromite
Chromite comes in dark brown to black mineral. It is an iron-chromium oxide, with traces of magnesium and aluminum. Its crystals are octahedral, but rare; it usually occurs as irregular, granular masses in association with igneous rocks, including ophiolites, which are segments of oceanic crust exposed on land by tectonic processes usually associated with plate convergence plate tectonics. Chromitite is an igneous rock composed chiefly of the mineral chromite.
The only commercial source of chromium and its compounds, chromite is used in the manufacture of refractory materials. Chromite has a variety of uses. Chromium is extracted from it to make stainless steel and other alloys for which resistance to oxidation and corrosion is important. Chromium is also used as plating and tanning agent. The mineral chromite is made into refractory lining for steel-making furnaces.