Chromite is an oxide mineral composed of chromium, iron and oxygen (FeCr2O4). It is a dark gray to black in color with a metallic to submetallic luster and a high specific gravity. It occurs in basic and ultrabasic igneous rocks and in the metamorphic and sedimentary rocks that are produced when chromite-bearing rocks are altered by heat or weathering.
Chromite is important because it is the only economic ore of chromium, an essential element for a wide variety of metal, chemical and manufactured products. Many other minerals contain chromium, but none of them are found in deposits that can be economically mined to produce chromium.
Properties of Chromite
Chromite can be challenging to identify. Several properties must be considered to differentiate it from other metallic ores. Hand specimen identification of chromite requires a consideration of: color, specific gravity, luster, and a characteristic brown streak. The most important clue to identifying chromite is its association with ultrabasic igneous rocks and metamorphic rocks such as serpentinite.
Chromite is sometimes slightly magnetic. This can cause it to be confused with magnetite. Chromite and ilmenite have very similar properties. Careful observations of hardness, streak and specific gravity are required to distinguish these minerals in hand specimens.
Uses
The following uses for chromium are gathered from a number of sources as well as from anecdotal comments. I'd be delighted to receive corrections as well as additional referenced uses (please use the feedback mechanism to add uses).
· used to harden steel, to manufacture stainless steel, and to form alloys
· used in plating to produce a hard, beautiful surface and to prevent corrosion.
· used to give glass an emerald green color. It is responsible for the green color of emeralds and the red color of rubies
· wide use as a catalyst
· dichromate’s such as K2Cr2O7 are oxidizing agents and are used in quantitative analysis and also in tanning leather
· lead chromate as chrome yellow is a pigment
· compounds are used in the textile industry as mordents
· used by the aircraft and other industries for anodizing aluminum
· the refractory industry uses chromite for forming bricks and shapes, as it has a high melting point, moderate thermal expansion, and stable crystalline structure
· tanning leather
Chrome ore grade 36% to 44% in size 0-400 mm