RocksdayGypsum vs Ulexite
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
A fibrous borate whose parallel fibers pipe light like fiber optics.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Key differences
- Satin spar gypsum is silky but doesn't transmit images.
Side by side
| Property | Gypsum | Ulexite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 2 | 2.5 |
| Luster | Vitreous to pearly | Silky |
| Streak | White | White |
| Colors | Clear, White, Brown | White |
| Crystal system | Monoclinic | Triclinic |
| Specific gravity | 2.31–2.33 | 1.95 |
| Formula | CaSO₄·2H₂O | NaCaB₅O₆(OH)₆·5H₂O |
| Found in | Naica, Mexico; White Sands, New Mexico | Boron, California; Turkey |
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 ulexite
- Silky white fibers in parallel bundles.
- Polished slabs show text from underneath on top.
- Light and soft.
Crystal system: Triclinic
Full Ulexite guide →More comparisons
Could you tell them apart from a blurry close-up?
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