Chromite
Chromite, Fe2+Cr2O4, is the chromium spinel: cubic, hardness 5.5, density 4.5 to 4.8, black with a brown streak. Ideal chromite is 46.46% chromium by mass.
Chromite is iron chromium oxide, Fe2+Cr2O4, a spinel-group mineral and an IMA species (G, 1845, France): cubic, hardness 5.5, density 4.5 to 4.8, black with a brown streak. Ideal chromite is 46.46% chromium by mass. USGS names South Africa the leading chromite ore producer, and the Handbook lists the Bushveld complex among its economic deposits.
In short
- The two-site check. Chromite and magnesiochromite share the spinel formula AB2O4 and differ on the A site: iron in chromite, magnesium in magnesiochromite. the IMA commission’s 1998 guidelines name a species by the atom making up at least 50% of a site. Worked on the Handbook of Mineralogy sheet’s printed formulas, the Bushveld analysis has 73.3% Fe on the A site and the Great Dyke analysis 54.0% Fe against 45.0% Mg: both chromite. The magnesiochromite sheet’s Kalarangi analysis has 88.0% Mg.
- Nine Cr2O4 rows. Three scans of the September 2026 IMA-CNMNC Master List find 9 rows whose formula ends in Cr2O4: chromite, magnesiochromite, manganochromite, zincochromite, cochromite, ellinaite (Ca), mariinskite (Be), and chenmingite and xieite, both written FeCr2O4 and both first described from meteorites (Morocco; China). Three rows share the bare iron formula, so FeCr2O4 alone does not name chromite.
- Documented failure: weight, streak and magnet. A 20.00 g piece reads 15.56 to 15.83 g in water as chromite and 15.44 to 15.72 g as magnesiochromite, an overlap of 15.56 to 15.72 g. Both sheets give a brown streak; chromite’s says some samples are weakly magnetic, magnesiochromite’s says weakly magnetic. A hand test cannot place a grain on either side of the 50% line; an analysis can.
- The chromium ledger. Worked on standard atomic weights, FeCr2O4 is 46.46% chromium and 67.90% Cr2O3, the sheet’s ideal column. Its Bushveld analysis has 52.17 wt% Cr2O3 (35.70% Cr), 76.8% of the ideal; the Great Dyke analysis 56.78 (38.85% Cr), 83.6%. USGS Mineral Commodity Summaries 2025, Chromium says chromium has no substitute in stainless steel, its leading end use.
- Where. The Distribution field opens widespread, and names Gassin, Var, France; large crystals from Hangha, Sierra Leone; Tiebaghi, New Caledonia; economic deposits in the Bushveld complex, South Africa; the Great Dyke, Zimbabwe; many localities in Turkey; Saranay in the Urals; the Moa district, Cuba; Luzon; and the Stillwater complex, Montana.
| Criterion | Chromite | Magnesiochromite | Hercynite | Magnetite | Separates chromite? |
|---|---|---|---|---|---|
| IMA row | Fe2+Cr2O4; G, 1845, France | MgCr2O4; G, 1873, Germany | Fe2+Al2O4; G, 1839, Czech Republic | Fe2+Fe3+2O4; G, 1845 | Only by analysis |
| A site / B site (ideal) | Fe2+ / Cr | Mg / Cr | Fe2+ / Al | Fe2+ / Fe3+ | Yes: the two-site check |
| Chromium by mass (ideal) | 46.46% | 54.08% | 0% | 0% | Only by analysis |
| Hardness | 5.5 | 5.5 to 7 | 7.5 to 8 | 5.5 to 6.5 | From hercynite |
| Density, measured | 4.5 to 4.8 | 4.39 to 4.67 | 4.40 | 5.175 | Not from magnesiochromite |
| 20.00 g piece in water | 15.56 to 15.83 g | 15.44 to 15.72 g | 15.45 g | 16.14 g | From magnetite (0.31 g) and hercynite (0.11 g); not magnesiochromite |
| Streak | Brown | Brown | Dark grayish green to dark green | Black | From hercynite and magnetite |
| Magnetism (sheet) | Some samples are weakly magnetic | Weakly magnetic | None printed | Strongly magnetic | From magnetite |
| Sheet analysis, two-site reading | Bushveld: Fe 73.3% of A, Cr 71.4% of B; Great Dyke: Fe 54.0%, Cr 73.9% | Kalarangi: Mg 88.0% of A, Cr 71.9% of B | Not worked | Not worked | Yes, with an analysis |
What is chromite? The chromium spinel
Chromite is iron chromium oxide, Fe2+Cr2O4, with the spinel structure. The Handbook of Mineralogy chromite sheet gives cubic, point group 4/m −3 2/m, with octahedral crystals modified by the cube or dodecahedron, to about 1 cm, and commonly fine granular, compact or massive material; twinning is on {111} by the spinel law. There is no cleavage, only a parting that may develop along {111}; it is brittle, hardness 5.5, Vickers 1278 to 1456 at a 100 g load, and measured density 4.5 to 4.8 against a calculated [5.12].
Colour and optics. The sheet gives black to brownish black, brown to brownish black on thin edges in transmitted light, with a brown streak and a metallic to submetallic lustre; it is isotropic, n = 2.08 to 2.16, and says some samples are weakly magnetic. What that means in practice, with the USGS separator figures, is on is chromite magnetic.
What the IMA list records. The September 2026 list gives chromite, Fe2+Cr2O4, status G (grandfathered, described before the IMA existed), 1845, with France as the country of first description. The sheet names it for its chromium content and places it in the spinel group, in series with magnesiochromite and hercynite. Its occurrence line reads: 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.
Chromite or magnesiochromite? The two-site check
Chromite is named by iron on the A site and chromium on the B site; magnesium in place of iron makes magnesiochromite. Nickel and Grice 1998, the IMA commission’s procedures and guidelines (Canadian Mineralogist 36, 913) says that where two types of atom share a structural site, the species is defined by the atom comprising at least 50% of that site. Chromite’s sheet prints the atomic proportions for both its analyses, so the check can be worked without a calculator beyond division.
Worked on the sheets. Bushveld complex, South Africa: (Fe2+0.74Mg0.27) on A and (Cr1.42Al0.40Fe3+0.15Ti0.01V0.01) on B, so iron is 73.3% of A and chromium 71.4% of B: chromite. Great Dyke, Zimbabwe: (Fe2+0.54Mg0.45Mn0.01) and (Cr1.47Al0.48Fe3+0.03Ti0.01), so iron 54.0% against magnesium 45.0%, chromium 73.9%: chromite, 4.0 points of iron above the line. The magnesiochromite sheet’s Kalarangi, Orissa analysis is (Mg0.88Fe2+0.12) with Cr 71.9% of B: magnesiochromite. Aluminium, which would make hercynite or spinel, is 20.1% and 24.1% of B in the two chromite analyses. Substitute any analysis in the same division.
Documented failure: the hand tests. On the sheets’ measured densities a 20.00 g piece reads 15.56 to 15.83 g in water as chromite and 15.44 to 15.72 g as magnesiochromite; the two windows share 15.56 to 15.72 g. Both streak brown, and both sheets record weak magnetism. Hardness 5.5 sits inside magnesiochromite’s 5.5 to 7. A Great Dyke grain at 54% iron and a magnesiochromite are the same black octahedron in the hand. The streak, weighing and scratch methods are on how to use a streak plate, how to measure specific gravity at home and how to test mineral hardness properly.
Which IMA minerals are chromium spinels? Nine Cr2O4 rows
The September 2026 IMA list has 9 rows whose formula ends in Cr2O4. Method: the list was converted with pdftotext -layout; a row parser, an independent scan of the second field of every line split on runs of two or more spaces, and a scan of every whitespace token all found the same 9, including chromite and magnesiochromite as a positive control. They are chromite Fe2+Cr2O4 (G, 1845, France), magnesiochromite MgCr2O4 (G, 1873, Germany), manganochromite Mn2+Cr2O4 (A, 1975-020, Australia), zincochromite ZnCr2O4 (A, 1986-015, Russia), cochromite CoCr2O4 (A, 1978-049, South Africa), ellinaite CaCr2O4 (A, 2019-091, Israel / Brazil), mariinskite BeCr2O4 (A, 2011-057, Russia), chenmingite FeCr2O4 (A, 2017-036, Morocco, meteorite) and xieite FeCr2O4 (A, 2007-056, China, meteorite).
What the count shows. Three of the nine are written with iron and chromium alone. The IMA guidelines say that minerals of the same composition whose structures are topologically different are separate species, with graphite and diamond as their example; the list gives chenmingite and xieite rows of their own, and this page claims nothing about their structures beyond that. A label reading FeCr2O4 therefore names a composition; a label reading chromite names the species. The wider spinel-family count, which also catches chrysoberyl, is on the spinel page and is not repeated here.
Where chromite sits. Of the two Cr2O4 rows with sheets cached here, chromite’s lists economic deposits; chromium spinel with magnesium dominant belongs to magnesiochromite, whose sheet lists dunites, serpentinites, kimberlites, lamproites and komatiites. Chromite’s own associates are olivine, enstatite, plagioclase, serpentine, magnetite, ilmenite, pyrrhotite, pentlandite and ulvöspinel.
Is chromite the ore of chromium? The chromium ledger
Chromite is chromium ore: USGS reports chromite ore production and names South Africa the leading producer. The USGS Mineral Commodity Summaries 2025, Chromium says South Africa was the leading chromite ore producer, that chromium has no substitute in stainless steel, the leading end use, or in superalloys, and that United States chromium resources are mostly in the Stillwater Complex in Montana, which is on the chromite sheet’s Distribution list. This page uses none of the summary’s market or tonnage figures.
The ledger, worked. On standard atomic weights FeCr2O4 is 46.46% chromium, or 67.90% Cr2O3 and 32.10% FeO, the figures in the sheet’s ideal column; MgCr2O4 is 54.08% chromium and 79.04% Cr2O3, as its sheet prints. Natural chromite carries less: the Bushveld analysis 52.17 wt% Cr2O3 (35.70% Cr), 76.8% of ideal, with 9.89 Al2O3, 5.88 Fe2O3 and 5.28 MgO; the Great Dyke analysis 56.78 (38.85% Cr), 83.6% of ideal. The shortfall is the aluminium, ferric iron and magnesium the two-site check counts.
Where chromite is found. The Distribution field: widespread; from Gassin, Var, France; large crystals from Hangha, Sierra Leone; at Tiebaghi, New Caledonia; as economic deposits in the Bushveld complex, Transvaal, South Africa; from the Great Dyke, Zimbabwe; from many localities in Turkey; at Saranay and elsewhere in the Ural Mountains, Russia; from the Moa district, northern Cuba; on Luzon, Philippines; and from the Stillwater complex, Montana. Any question about handling chromium minerals belongs on toxic minerals in a collection; nothing on this page is health or safety advice. The rest of the reference section is at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.