RocksdayChromite vs Magnetite
How to tell them apart
The only ore of chromium: a heavy black oxide found in ultramafic rocks.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
The most magnetic naturally occurring mineral. Black, heavy and often found as eight-sided crystals or as black sand on beaches.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Quick tests
- Magnet: A magnet sticks to Magnetite but not to Chromite.
- Streak (rub on unglazed porcelain): Chromite leaves a brown streak; Magnetite leaves black.
- Luster: Magnetite looks metallic; Chromite doesn't.
Key differences
- Magnetite is strongly magnetic with a black streak.
Side by side
| Property | Chromite | Magnetite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 5.5 | 5.5–6.5 |
| Luster | Submetallic | Metallic |
| Streak | Brown | Black |
| Colors | Black | Black |
| Crystal system | Cubic | Cubic |
| Specific gravity | 4.5–4.8 | 5.1–5.2 |
| Formula | FeCr₂O₄ | Fe₃O₄ |
| Found in | Bushveld Complex, South Africa; Kazakhstan | Kiruna, Sweden; Adirondack Mountains, New York |
Properties that are the same for both are grayed out.
How to identify chromite
- Black, heavy grains or layers in dark rock.
- Brown streak.
- Weakly magnetic at most.
Crystal system: Cubic
Full Chromite guide →How to identify magnetite
- Strongly attracts a magnet (some pieces are magnets themselves).
- Black streak.
- Heavy, black, metallic.
- Octahedral crystals when well-formed.
Crystal system: Cubic
Full Magnetite guide →More comparisons
Could you tell them apart from a blurry close-up?
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