Selenite vs Gypsum
Selenite and Gypsum are easy to confuse. Here’s how they stack up on the properties that actually separate them.
| Selenite | Gypsum | |
|---|---|---|
| Also known as | Gypsum (Gypsum family) | — |
| Colour | White, Clear | White, Clear, Yellow, Blue |
| Mohs hardness | 2 | 1.5–2 (defining mineral for 2) |
| Lustre | Vitreous Satin spar gypsum: pearly | Vitreous to silky, pearly, or waxy |
| Streak | White | White |
| Crystal system | Monoclinic (2/m) Space group: A2/a | Monoclinic |
| Transparency | Transparent Satin spar gypsum: translucent to opaque | Transparent to translucent |
| Cleavage | [010] Perfect, [100] Distinct, [011] Distinct | Perfect on {010}, distinct on {100} |
| Fracture | Micaceous Satin spar gypsum: fibrous | Conchoidal on {100}, splintery parallel to [001] |
| Chemical formula | CaSO 4 ·2H 2 O | — |
| Specific gravity | 2.9 | 2.31–2.33 |
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Frequently asked questions
What's the easiest way to tell Selenite from Gypsum?
Compare lustre, streak and crystal habit side by side — colour alone won't settle it.