Is chromite magnetic?
Weakly, in some samples. The Handbook says some chromite samples are weakly magnetic; USGS pulled 9 samples at 0.05 to 0.50 amp, where magnetite needed 0.01.
Weakly, and not always. The chromite sheet says some samples are weakly magnetic. USGS Open-File Report 99-529 pulled 9 chromite samples at 0.05 to 0.50 amp on a laboratory separator, best 0.30 to 0.40: paramagnetic by its definitions, where magnetite came out at 0.01. Chromite, Fe2+Cr2O4, hardness 5.5, is 24.95% iron by mass.
In short
- The sample clause. The Handbook of Mineralogy chromite sheet does not say chromite is magnetic; it says some samples are weakly magnetic. A piece that ignores a magnet can still be chromite, and a weak response is consistent with it. Of the sheets in the table, only magnetite’s says strongly magnetic.
- Measured. USGS Open-File Report 99-529, Table 1 pulled 9 chromite samples at 0.05 to 0.50 amp, best 0.30 to 0.40, on a Frantz isodynamic separator. USGS calls ferromagnetic only what is strongly attracted to a magnet, like a piece of iron, naming magnetite, maghemite, pyrrhotite and pentlandite; paramagnetic minerals separate at up to 1.70 amps. Chromite is paramagnetic by those definitions.
- The spinel rows. Matched by script to IMA formulas, 6 rows of Table 1 are spinel-formula oxides. By best range: magnetite Fe2+Fe3+2O4 at 0.01 amp; franklinite ZnFe3+2O4 0.10 to 0.20; chromite Fe2+Cr2O4 and hercynite Fe2+Al2O4 0.30 to 0.40; gahnite ZnAl2O4 0.40 to 0.50; spinel MgAl2O4 0.50 to 1.00. The two with ferric iron in the formula come first; the two with no iron in the formula come last.
- Documented failure: hercynite. Hercynite is 32.13% iron by mass against chromite’s 24.95%, yet both have a best range of 0.30 to 0.40 amp, and hercynite’s total range, 0.10 to 0.50, sits inside chromite’s. Iron content does not order them and the separator cannot split them. The sheets can: hercynite is hardness 7.5 to 8 with a dark green streak; chromite 5.5, brown.
- The 0.05-amp contact. Chromite’s lowest extraction, 0.05 amp, is magnetite’s highest. USGS warns that micro-inclusions of magnetite make the lower limit of extraction difficult or impossible to determine. A strong snap to a hand magnet is what the magnetite sheet describes, not what the chromite sheet does.
| Name | Formula (IMA) | Iron in formula | Iron by mass | Total range (amp) | Best range (amp) | Samples | Handbook magnetism | Streak (sheet) |
|---|---|---|---|---|---|---|---|---|
| Magnetite | Fe2+Fe3+2O4 | Fe2+ and Fe3+ | 72.36% | Below 0.01 to 0.05 | 0.01 | 6 | Strongly magnetic | Black |
| Franklinite | ZnFe3+2O4 | Fe3+ | 46.33% | 0.01 to 0.40 | 0.10 to 0.20 | 7 | No sheet (404) | No sheet |
| Chromite | Fe2+Cr2O4 | Fe2+ | 24.95% | 0.05 to 0.50 | 0.30 to 0.40 | 9 | Some samples are weakly magnetic | Brown |
| Hercynite | Fe2+Al2O4 | Fe2+ | 32.13% | 0.10 to 0.50 | 0.30 to 0.40 | 2 | None printed | Dark grayish green to dark green |
| Gahnite | ZnAl2O4 | None | 0% | 0.20 to 0.70 | 0.40 to 0.50 | 2 | None printed | Gray |
| Spinel | MgAl2O4 | None | 0% | 0.10 to 1.10 | 0.50 to 1.00, depends on chemistry | 3 | None printed | White |
| Magnesiochromite (sheet only) | MgCr2O4 | None | 0% | Not in Table 1 | Not in Table 1 | - | Weakly magnetic | Brown |
Is chromite magnetic? What the Handbook sheet says
The chromite sheet says some samples are weakly magnetic, and nothing stronger. The Handbook of Mineralogy chromite sheet gives Fe2+Cr2O4, cubic, octahedral crystals to about 1 cm and commonly granular or massive, hardness 5.5, density 4.5 to 4.8, black to brownish black with a brown streak, and, in its physical-properties line, some samples are weakly magnetic. Read as printed, that is a statement about some samples, not a property of the species: the sheet does not promise a response.
Its neighbours, as printed. The magnesiochromite sheet says weakly magnetic, without the qualifier; the magnetite sheet says strongly magnetic; the hercynite, gahnite and spinel sheets print nothing on magnetism. The worked comparison of magnetite against chromite, ilmenite and hematite by streak and magnet is on magnetite and is not repeated here. The species facts for chromite are on chromite.
What this page does not claim. Neither the sheet nor USGS gives a cause for chromite’s weak response specifically. USGS says, in general, that chemistry is the main factor controlling magnetic susceptibility, and that iron and copper are two elements responsible for paramagnetic susceptibility in some minerals. That is as far as the sources go.
How magnetic is chromite? 0.05 to 0.50 amp on the USGS separator
Chromite was pulled at 0.05 to 0.50 amp, best 0.30 to 0.40, across 9 samples. USGS Open-File Report 99-529 (Rosenblum and Brownfield) ran 1084 samples of 378 mineral species through Frantz isodynamic separators, on grains of 125 to 150 micrometres at a 15° side tilt. For paramagnetic minerals the field current started at 0.10 amp and rose in 0.10-amp steps; for the few ferromagnetic species it started at about 0.01 amp, then 0.025, 0.05 and 0.10.
The definitions. USGS calls ferromagnetic the minerals strongly attracted to a magnet, like a piece of iron, and names magnetite, maghemite, pyrrhotite and pentlandite. Paramagnetic minerals are less magnetic and separable at up to 1.70 amps, the greatest value reached on its separators; diamagnetic minerals are not pulled at 1.70. Chromite’s whole range lies in the paramagnetic band. Magnetite came out at below 0.01 to 0.05 amp, best 0.01, which is the figure quoted on magnetite.
Documented limit: the 0.05-amp contact. Chromite’s lowest figure, 0.05 amp, is magnetite’s highest. The report warns that when micro-inclusions of magnetite or other ferromagnetic minerals are present, the actual lower limit of extraction is difficult or impossible to determine. The same cautions, and the carbonate and copper results, are on is siderite magnetic and is malachite magnetic; their row counts are not repeated here.
Which spinels does a magnet pull first? The spinel rows
Among the six spinel-formula oxides USGS measured, the ones with ferric iron come first and the ones with no iron in the formula come last. Method: every row of Table 1 was matched by script to its September 2026 IMA formula, and the rows written as one cation, two of a second and O4 were kept: magnetite, franklinite, chromite, hercynite, gahnite and spinel. Ilmenite, at 0.20 to 0.30 best, is Fe2+Ti4+O3 on the IMA list and is left out. In order of best range: magnetite 0.01; franklinite, ZnFe3+2O4, 0.10 to 0.20; chromite and hercynite, both Fe2+ on the A site, 0.30 to 0.40; gahnite, ZnAl2O4, 0.40 to 0.50; spinel, MgAl2O4, 0.50 to 1.00, which USGS marks depends on chemistry.
Documented failure: iron by mass does not order them. Worked from the IMA formulas: magnetite 72.36% iron, franklinite 46.33%, hercynite 32.13%, chromite 24.95%, gahnite and spinel none. Hercynite carries more iron than chromite and lands on exactly the same best range, 0.30 to 0.40, with its total range inside chromite’s. Gahnite and spinel, iron-free as written, are still pulled; the report gives no cause for these two rows, and this page offers none.
What separates chromite from hercynite instead. The sheets: hercynite is hardness 7.5 to 8 with a dark grayish green to dark green streak; chromite is 5.5 with a brown streak. The streak method is on how to use a streak plate and the scratch method on how to test mineral hardness properly.
Can a magnet tell chromite from magnetite? Only the strong end
A hand magnet separates magnetite, and only magnetite, from the black spinels. Neither source tests a hand magnet; USGS describes ferromagnetic minerals as strongly attracted to one. A black octahedron that snaps hard to a magnet is behaving as the magnetite sheet describes. A faint drag, or nothing, is what the chromite sheet allows, and magnesiochromite’s sheet records weak magnetism as well. A strong pull from a grain labelled chromite is behaviour neither the chromite sheet nor USGS’s chromite row describes; the USGS warning about magnetite micro-inclusions is the documented reason to look for a second mineral.
The decision, in order. Streak first: brown for chromite and magnesiochromite, black for magnetite, dark green for hercynite. Hardness second: 5.5 for chromite, 7.5 to 8 for hercynite. The magnet last, and only to confirm magnetite. The two-site check that separates chromite from magnesiochromite needs an analysis and is on chromite. How other species answer the same question is on which minerals are magnetic and is tetrahedrite magnetic.
Out of scope. Chromium compounds raise handling questions that belong on toxic minerals in a collection; nothing on this page is health or safety advice. Game references to chromite are not covered. The magnetism questions are indexed at the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.