Gypsum

CaSO4 · 2H2O

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The reference mineral for hardness 2 on the Mohs scale, gypsum is a very soft hydrated calcium sulfate (CaSO4 2H2O) and one of the most widely used industrial minerals. It crystallizes in the monoclinic system as tabular, prismatic, or massive forms, showing a vitreous luster, a white streak, and perfect {010} cleavage. Its varieties include transparent selenite, fibrous satin spar, and fine-grained alabaster, with a specific gravity near 2.32. Gypsum forms extensively in evaporite settings and supplies the raw material for plaster and wallboard, industries that consume it in enormous quantities. A specific gravity near 2.32 and the ease with which a fingernail scratches it confirm identification.

Gypsum is a very soft mineral, the reference for hardness 2 on the Mohs scale. Its varieties include selenite (colorless transparent crystals), satin spar (fibrous), and alabaster (fine-grained massive). It is one of the most widely used industrial minerals.

Crystal System Monoclinic
Mineral Class 07 Sulfates, Chromates, Molybdates, and Tungstates
Mohs Hardness 1.5-2.0
Specific Gravity 2.31-2.33
Color Colorless, white, gray, yellow, brown
Luster Vitreous
Streak White
Cleavage Perfect {010}
Fracture Conchoidal
Transparency Transparent
Crystal Habit Tabular, prismatic, massive

Mohs Hardness

Mohs Hardness: 1.5 – 2.0
1 Soft10 Hard
Gypsum has a Mohs hardness of 1.5–2 on the 1–10 mineral hardness scale.
Mohs Hardness Reference Mineral
1 Talc
2 Gypsum
3 Calcite
4 Fluorite
5 Apatite
6 Orthoclase
7 Quartz
8 Topaz
9 Corundum
10 Diamond

Crystal System

Monoclinic
Gypsum crystallizes in the Monoclinic crystal system.
Property Value
Crystal System Monoclinic
Axial Relationships a ≠ b ≠ c, α = γ = 90°, β ≠ 90°

Frequently Asked Questions

What is the hardness of Gypsum?
Gypsum has a Mohs hardness of 1.5-2.0.
What crystal system does Gypsum belong to?
Gypsum crystallizes in the Monoclinic crystal system.
What color is Gypsum?
Gypsum is typically Colorless, white, gray, yellow, brown.
What type of luster does Gypsum have?
Gypsum exhibits a Vitreous luster.
What is the chemical formula of Gypsum?
The chemical formula of Gypsum is CaSO4 · 2H2O.