RocksdayMagnetite vs Uraninite
How to tell them apart
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
The main ore of uranium — heavy, black and radioactive.
Photo: Geomartin, CC BY-SA 3.0
Quick tests
- Magnet: A magnet sticks to Magnetite but not to Uraninite.
- Streak (rub on unglazed porcelain): Magnetite leaves a black streak; Uraninite leaves brownish black.
- Heft: Uraninite feels noticeably heavier for its size (specific gravity 6.5–10.9 vs 5.1–5.2).
- Luster: Magnetite looks metallic; Uraninite doesn't.
Key differences
- Magnetite is magnetic and not radioactive.
Side by side
| Property | Magnetite | Uraninite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 5.5–6.5 | 5–6 |
| Luster | Metallic | Submetallic to pitchy |
| Streak | Black | Brownish black |
| Colors | Black | Black, Brown |
| Crystal system | Cubic | Cubic |
| Specific gravity | 5.1–5.2 | 6.5–10.9 |
| Formula | Fe₃O₄ | UO₂ |
| Found in | Kiruna, Sweden; Adirondack Mountains, New York | Jáchymov, Czech Republic; Shinkolobwe, DR Congo |
Properties that are the same for both are grayed out.
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 →How to identify uraninite
- Pitch-black, heavy masses.
- Strongly radioactive.
- Often with bright yellow or green alteration crusts.
Crystal system: Cubic
Full Uraninite guide →More comparisons
Could you tell them apart from a blurry close-up?
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