RocksdayGypsum vs Muscovite
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
Light-colored mica that peels into paper-thin, transparent and flexible sheets. Its flakes are what make many rocks glitter.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Key differences
- Mica peels into elastic sheets that spring back; gypsum flakes stay bent.
- Gypsum flakes bend but don't spring back.
Side by side
| Property | Gypsum | Muscovite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 2 | 2–2.5 |
| Luster | Vitreous to pearly | Vitreous to pearly |
| Streak | White | White |
| Colors | Clear, White, Brown | Clear, Silver, Brown |
| Crystal system | Monoclinic | Monoclinic |
| Specific gravity | 2.31–2.33 | 2.76–2.88 |
| Formula | CaSO₄·2H₂O | KAl₂(AlSi₃O₁₀)(OH)₂ |
| Found in | Naica, Mexico; White Sands, New Mexico | Pegmatites of North Carolina; New Hampshire |
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 muscovite
- Peels into thin sheets that spring back when bent.
- Transparent to silvery and sparkly.
- Soft — scratched by a fingernail across the sheets.
- Stacked 'books' of sheets in pegmatites.
Crystal system: Monoclinic
Full Muscovite guide →More comparisons
Could you tell them apart from a blurry close-up?
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