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The Mineral chromite

Chromite with Serpentine veins

Chromite,  the principle ore of the element chromium, is a commercially valuable mineral. However, due to mining restrictions and the fact that Chromite is not commonly found in crystallized form, it is not well-represented in mineral collections. Chromite is isomorphous with the mineral Magnesiochromite and is easily confused with it, as they occur in the same environments.

Chemical Formula

FeCr2O4

Color

Brownish-black to greenish-black

Crystal System

Isometric

Properties

Streak
Dark brown
Hardness
5.5
Transparency
Opaque
Specific Gravity
4.2 - 5.0
Luster
Metallic to dull
Cleavage
None. May exhibit parting.
Fracture
Conchoidal to uneven
Tenacity
Brittle
Other ID Marks
Is paramagnetic, often being attracted to magnetic fields.

Crystal Habits

Crystals, which are octahedral, are not common. Microscopic dodecahedral crystals are also known. Most commonly grainy, massive, in veins, as rounded pebbles, in rounded grains, and in nodular blobs embedded in rock.

3D Crystal Atlas

Additional Information

Composition
Iron chromium oxide, often with some magnesium, sometimes with aluminum. Forms a series with the rarer mineral Magnesiochromite.
In Group
Oxides; Multiple Oxides
Striking Features
Streak, hardness, and slight attraction to magnetic fields.
Environment
In metamorphic Serpentine deposits, and also in ultrabasic igneous rocks, and in placer deposits. May also occur in meteorites.
Rock Type
Igneous, Metamorphic, Meteoric

Varieties

 -   Magnesium-rich variety of Chromite where the iron is replaced by magnesium. Magnesiochromite is sometimes classified as a variety of Chromite, but is scientifically recognized as an individual mineral.

Uses

Chromite is the main ore of the element chromium.

Noteworthy Localities

There are not many occurrences of collectible Chromite specimens, as this mineral mostly occurs in microcrystalline or crudely crystallized form in commercially exploited deposits. Thus, specimens of this mineral are not commonly encountered. Large commercial deposits of Chromite exist in Russia, India, Kazakstan, the Philippines, New Caledonia, Kosovo, Zimbabwe, Turkey, Brazil, and Cuba.

Crystallized Chromite specimens are rare, although small octahedral crystals occur with Uvarovite in Outokumpu, Finland. An isolated find of sharp octahedral crystals, perhaps the best for this species, came from Hangda, Kenema District, Sierra Leone. The Moa Mine, in Oriente Province, Cuba, has produced euhedral crystals up to 2 cm.

In the U.S., Chromite has come from the Soldier's Delight Quarry and the Bare Hills, Baltimore Co., Maryland; as well as the Wood's Mine, near Texas, Lancaster Co., Pennsylvania. Small crystals also occur with Serpentine in Staten Island (Richmond Co.), New York; and in Castle Point, Hoboken, Hudson Co., New Jersey. Other Chromite occurrences are the Stillwater Complex, Stillwater Co., Montana; and the Day Book Quarry, Toecane, Yancey Co., North Carolina.

Common Mineral Associations

Serpentine, Calcite, Chlorite, Talc, Olivine, Magnetite, Uvarovite

Distingushing Similar Minerals

Magnetite - Has a darker streak.
Magnesiochromite - Very difficult to distinguish, although has a grayish streak.

chromite Photos



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