RocksdayGypsum vs Talc
How to tell them apart
A soft, water-bearing calcium sulfate formed as seawater and lakes evaporate. Clear crystals are called selenite; sand-filled rosettes are 'desert roses'.
Photo: Didier Descouens, CC BY-SA 4.0
The softest mineral, number 1 on the Mohs scale. It feels soapy or greasy and leaves powder on your fingers.
Photo: Unknown, Public domain
Key differences
- Gypsum isn't greasy and is a bit harder.
Side by side
| Property | Gypsum | Talc |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 2 | 1 |
| Luster | Vitreous to pearly | Pearly to greasy |
| Streak | White | White |
| Colors | Clear, White, Brown | White, Green, Gray |
| Crystal system | Monoclinic | Monoclinic |
| Specific gravity | 2.31–2.33 | 2.7–2.8 |
| Formula | CaSO₄·2H₂O | Mg₃Si₄O₁₀(OH)₂ |
| Found in | Naica, Mexico; White Sands, New Mexico | Vermont; Montana |
Properties that are the same for both are grayed out.
How to identify gypsum
- Scratches with a fingernail (hardness 2).
- Clear blades that bend slightly before snapping.
- Doesn't fizz in acid.
- Feels warm, not cold like glass.
Crystal system: Monoclinic
Full Gypsum guide →How to identify talc
- Easily scratched by a fingernail.
- Slippery, soapy feel.
- Pearly sheen on flaky surfaces.
- Flakes don't spring back when bent.
Crystal system: Monoclinic
Full Talc guide →More comparisons
Could you tell them apart from a blurry close-up?
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