RocksdayCuprite vs Proustite
How to tell them apart
Copper oxide forming deep red cubes and octahedrons, sometimes as hair-like 'chalcotrichite'.
Photo: Didier Descouens, CC BY-SA 3.0
A translucent scarlet silver sulfosalt that darkens when exposed to light.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Quick tests
- Fingernail: A fingernail scratches Proustite (Mohs 2–2.5) but not Cuprite (Mohs 3.5–4).
- Streak (rub on unglazed porcelain): Cuprite leaves a brownish red streak; Proustite leaves scarlet.
Key differences
- Cuprite is darker and cubic.
Side by side
| Property | Cuprite | Proustite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 3.5–4 | 2–2.5 |
| Luster | Adamantine to submetallic | Adamantine |
| Streak | Brownish red | Scarlet |
| Colors | Red, Black | Red |
| Crystal system | Cubic | Trigonal |
| Specific gravity | 6.1–6.15 | 5.55–5.64 |
| Formula | Cu₂O | Ag₃AsS₃ |
| Found in | Onganja, Namibia; Bisbee, Arizona | Chañarcillo, Chile; Freiberg, Germany |
Properties that are the same for both are grayed out.
How to identify cuprite
- Deep red, glinting crystals that can look almost black.
- Heavy.
- Brownish-red streak.
Crystal system: Cubic
Full Cuprite guide →How to identify proustite
- Translucent scarlet crystals with a brilliant luster.
- Darkens to gray in light.
- Scarlet streak.
Crystal system: Trigonal
Full Proustite guide →More comparisons
Could you tell them apart from a blurry close-up?
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