Mineral Information and Data:

Fe2+Cr2O4 [CNMNC approved formula]

Named in allusion to its composition.

IMA status : Valid species (Pre-IMA 1845) Grandfathered
(8th edition) :  
  (07) Multiple Oxides
  (07.02) (A+ B++)2 X4 Spinel group
  (07.02.03) (Chromium subgroup)
(10th edition) :
  (04) Oxides and Hydroxides
  (04.B) Metal:Oxygen = 3:4 and similar
  (04.BB) With only medium-sized cations
Crystal system: Cubic System
Point group (H-M): m3m (or 4/m 3 2/m) — hexoctahedral
Unit cell: a = 8.344 Å
Crystal Habit: Crystals octahedral; massive, compact to fine granular
Color: Black to brownish black; brown to brownish black on thin edges in transmitted light; in reflected light, gray-white with a brownish tint and brownish red internal reflections.
Diaphaneity: Opaque
Luster: Metallic to submetallic
Hardness (Mohs): 5.5
Measured Density: 4.5 to 4.8 g/cm3
Cleavage: None
Tenacity: Brittle
Fracture: Uneven
Streak: Brown
Polymorphism and Series: Series with magnesiochromite and with hercynite
Geologic Setting: A cumulus mineral in ultramafic portions of layered mafic igneous rocks; an accessory mineral in alpine-type peridotites; also detrital. Common in all meteorites, except carbonaceous chondrites, and in lunar mare basalts.
Mineral Association: Olivine, enstatite, plagioclase, serpentine, magnetite, ilmenite, pyrrhotite,
pentlandite, ulvöspinel.
Ore deposits: Chief source of chromium. Usually found in large layered intrusives and serpentine bodies.
Other Properties: Paramagnetic (weakly attracted to magnetic fields). Gemstone Unlikely Available.
Comments: Usually contains some Mg and Al. Much of the mineral referred to as "chromite" in economic geology papers and mining statistics is actually the related species Magnesiochromite, and not technically the species Chromite.


Origin: Clear Creek area, New Idria District, San Benito Co., California, U.S.A.
Sample size: 5.7 x 4.9 x 4.1 cm
Photo: Dan Weinrich


(zoom-in of above)


Origin: Onverwacht, Eastern Bushvel, RSA
Sample size: 3 x 5 cm
Photo: Diederik Visser