Rock IdentifierSelenite & Gypsum
Key takeaways
- Selenite is a crystalline form of gypsum, Mohs 2 — a fingernail scratches it.
- It's water-soluble over time and should never be soaked or cleaned wet.
- Its softness and satiny sheen distinguish it from harder clear minerals.
What it is
Selenite is a clear, crystalline variety of gypsum (hydrated calcium sulfate). Gypsum also appears as fibrous 'satin spar' (with a moving cat's-eye sheen), granular alabaster, and the spectacular 'desert rose' clusters. All are very soft — Mohs 2 — and lightweight.
How to recognize it
The giveaway is softness: your fingernail scratches gypsum easily, which almost nothing else clear does (quartz and calcite are much harder). Selenite is often colorless and transparent with a pearly-to-glassy luster and can be peeled or bent in thin sheets. Satin spar shows a silky, shifting band of light along its fibers.
Care — keep it dry
Gypsum is slightly water-soluble and structurally soft, so water can dull, etch, or slowly dissolve it, and it scratches at the lightest contact. Never soak or wet-clean selenite — dust it with a dry, soft brush instead. Store it away from harder minerals and humidity. Its beauty is real, but it's one of the most fragile stones a beginner will handle.
