What Is Chromate?

Commonly found in meteorites and metamorphic rocks such as serpentites
Name: Chromite
Chemistry: FeCr₂O₄
Color: Deep dark black, brownish black
Hardness: 5.5
Specific Gravity: 4.5-4.8
Crystals: Isometric
Accompanied by: Anorthite, Biotite, Magnetite, Magnesium, Olivine, Serpentine, Talc, Uvarovite, Pyroxenes
Fracture: Uneven / conchoidal
Luster: Metallic to greasy
Cleavage: None
Used in a wide range of industrial process. Natural Chromite contains some magnesium. It is weakly magnetic and an octahedral parting is sometimes seen
• Chemical Formula: FeCr₂O₄, Iron Chromium Oxide.
• Class: Oxides and Hydroxides
• Group: Spinel
• Uses: The principle ore of chromium, as a refractory component, as a dye and as mineral specimens.
• Specimens
Chromite is the most important ore of chromium from which it derives its name. Chromium is an important metal and has a wide range of industrial uses.
Chromite forms in deep ultra-mafic magmas and is one of the first minerals to crystallize. It is because of this fact that Chromite is found in some concentrated ore bodies. While the magma is slowly cooling inside the Earth's crust, chromite crsytals are forming and because of their density, fall to the bottom and are concentrated there.
Although its primary origin is ultra-mafic rocks such as peridotites, Chromite is also found in metamorphic rocks such as serpentites. 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 serpentine, 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.

Chromite Packing

Chromate Physical Properties

General Properties of Chromate Fe++Cr₂O₄

Empirical Formula: Fe₂+Cr₂O₄
Environment: Cummulate mineral found in ultramafic portions of layered mafic intrusions. Common in meteorites.
IMA Status: Valid Species (Pre-IMA)
Name Origin: Named after its chemical composition.
Synonym: Chrome iron ore, Chromic iron, Ferrichromite-magnetic, altered, ICSD 20819

chromite Crystallography

Optical Properties of Chromate

Calculated Properties of Chromate

Chromate Classification

Spinel Group

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