Gypsum
| Colour | White, Clear, Yellow, Blue |
|---|---|
| Mohs hardness | 1.5–2 (defining mineral for 2) |
| Lustre | Vitreous to silky, pearly, or waxy |
| Streak | White |
| Crystal system | Monoclinic |
| Transparency | Transparent to translucent |
| Cleavage | Perfect on {010}, distinct on {100} |
| Fracture | Conchoidal on {100}, splintery parallel to [001] |
| Specific gravity | 2.31–2.33 |
What is Gypsum?
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk chalk. Gypsum also crystallizes as translucent crystals of selenite. It forms as an evaporite mineral and as a hydration product of anhydrite. The Mohs scale of mineral hardness defines gypsum as hardness value 2 based on scratch hardness comparison.
How to identify Gypsum
- Lustre: Vitreous to silky, pearly, or waxy.
- Hardness: Mohs 1.5–2 (defining mineral for 2) — soft; a knife will scratch it.
- Streak: White.
- Habit: Monoclinic crystal system.
Gypsum in different forms
Stones often confused with Gypsum
Frequently asked questions
How hard is Gypsum?
Gypsum is Mohs 1.5–2 (defining mineral for 2) on the hardness scale.
What colour is Gypsum?
Gypsum is typically white, clear, yellow, blue (Colorless (in transmitted light) to white; often tinged other hues due to impurities; may be yellow, tan, blue, pink, da).