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Chromite Mineral Facts:

Chemical Formula: FeCr₂O₄
Oxide of iron and chromium, Chromium oxide 68.0%.The iron may be partly replaced by magnesium and the chromium by aluminum and ferric iron.

Colors: Black to brownish black. Streak - Dark Brown

Hardness: 5.5

Density: 4.6

Cleavage: It has a conchoidal or uneven fracture and no distinct cleavage.

Crystallography: Isometric, Habit Octahedral  
Crystals small and rare. Occurs in octahedrons, but is commonly found massive, having a granular or compact structure.

Luster:. Weak submetallic luster, often faint.

Optics: (Refractive Index)  = Opaque
 

Composition, Structure and Associated Minerals:
A common constituent of peridotite rocks and the serpentines derived from them.  The mineral is found not only as crystals embedded in the rock mass, but also as nodules in it and as veins traversing it. One of the first minerals to separate from a cooling rock magma, and its large ore deposits are thought to have been derived by such magmatic differentiation. It is probably in all cases a segregation from the magma producing the rock. Associated with chrysolite asbestos, serpentine, corundum, etc  Being very durable, chromite occurs in detrital deposits and in a few places the mineral occurs in the form of sand on beaches.

Identification and Diagnostics
It resembles magnetite and franklinite in appearance. Chromite is easily distinguished from all other minerals but picotite by its crystallization and its reaction for chromium. It is distinguished from picotite by its inferior hardness and its higher specific gravity. When finely powdered and fused on charcoal with sodium carbonate gives a magnetic residue. Imparts a green color to the borax and salt of phosphorus beads (a test for chromium).  It is usually nonmagnetic, but some specimens show slight magnetism because of the admixture of magnetite with chromite.

Industrial Uses of Chromite
Chromite is the sole source of the metal chromium, which is the chrome-iron alloy employed in the manufacture of special grades of steel. Chromium salts are used in tanning and as pigments and plating. The crude ore, mixed with coal-tar, kaolin, bauxite, or some other ingredient, is molded into bricks and burned, after which the bricks are used as linings in metallurgical furnaces. These bricks stand rapid changes of temperature and are not attacked by molten metals.

It is found at many locations but only sparingly in the United States. In the United States the mineral is known at several points in a belt of serpentine on the east side of the Appalachian Mountains, and at many points in the Rocky Mountains, the Sierra Nevada and the Coast Ranges. It has been mined at Bare Hills, Maryland; in Siskiyou, Tehama and Shasta Counties, California; in Converse County, Wyoming; and in Chester and Delaware Counties, Pennsylvania; and; in 1914, some was washed from chrome sand at Baltimore, Maryland. Small amounts were historically produced in the certain states of the US, including Pennsylvania, Maryland,North Carolina Montana, Oregon and California and Wyoming.

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