This article is about the mineral. For the chromium(III) cation and its salts, see Chromite (compound).
Chromite
Octahedral chromite crystal from the Freetown Layered Complex in Sierra Leone, Africa (size: 1.3 x 1.2 x 1.2 cm)
General
Category
Oxide minerals Spinel group Spinel structural group
Formula (repeating unit)
(Fe, Mg)Cr2O4
IMA symbol
Chr[1]
Strunz classification
4.BB.05
Crystal system
Isometric
Crystal class
Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group
Fd3m (no. 227)
Unit cell
a = 8.344 Å; Z = 8
Identification
Color
Black to brownish black; brown to brownish black on thin edges in transmitted light
Crystal habit
Octahedral rare; massive to granular
Twinning
Spinel law on {Ill}
Cleavage
None, parting may develop along {III}
Fracture
Uneven
Tenacity
Brittle
Mohs scale hardness
5.5
Luster
Resinous, Greasy, Metallic, Sub-Metallic, Dull
Streak
Brown
Diaphaneity
Translucent to opaque
Specific gravity
4.5–4.8
Optical properties
Isotropic
Refractive index
n = 2.08–2.16
Other characteristics
Weakly magnetic
References
[2][3][4][5]
Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite (MgCr2O4).[6] A substitution of the element aluminium can also occur, leading to hercynite (FeAl2O4).[7] Chromite today is mined particularly to make stainless steel through the production of ferrochrome (FeCr), which is an iron-chromium alloy.[8]
Chromite grains are commonly found in large mafic igneous intrusions such as the Bushveld in South Africa and India. Chromite is iron-black in color with a metallic luster, a dark brown streak and a hardness on the Mohs scale of 5.5.[9]
^Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. "Chromite". Handbook of Mineralogy(PDF). Mineralogical Society of America. p. 122. Archived from the original (PDF) on 13 May 2021. Retrieved 13 April 2019.
^Klein, Corneis; Hurlbut, Cornelius S. (1985). Manual of Mineralogy (20th ed.). Wiley. pp. 312–313. ISBN 0471805807.
^"Chromite Mineral Data". Webmineral data. Retrieved 13 April 2019.
^Hudson Institute of Mineralogy. "Chromite: Mineral information, data and localities". Mindat.org. Retrieved 13 April 2019.
^Hudson Institute of Mineralogy. "Chromite-Magnesiochromite Series: Mineral information, data and localities". Mindat.org. Retrieved 13 April 2019.
^Hudson Institute of Mineralogy. "Chromite-Hercynite Series: Mineral information, data and localities". Mindat.org. Retrieved 13 April 2019.
^"Potential Toxic Effects of Chromium, Chromite Mining and Ferrochrome Production: A Literature Review" (PDF). May 2012. Retrieved March 15, 2019.
^Hurlbut, Cornelius S.; Sharp, W. Edwin; Dana, Edward Salisbury (1998). Dana's minerals and how to study them (4th. ed.). New York: Wiley. ISBN 0471156779. OCLC 36969745.
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