Sulfates: Anhydrite

Composition: CaSO₄

Crystal system: Orthorhombic; usually massive, granular or fibrous

6.3.1
cleavable anhydrite

Properties:

• Vitreous to silky lustre
• Variable color; colorless, white, cream, pink, grey, blue
• White streak
• Knife scratches very easily; fingernail does not scratch (Mohs Hardness 3.5)
• Average density
• Three good cleavages at 90^o.
• Cleaves rather than fractures unless finegrained
• Not ferromagnetic
• Soluble in hot hydrochloric acid (HCl)

Occurrence:

Anhydrite may precipitate directly from seawater or form by the dehydration of gypsum (CaSO₄.2H₂O) as a result of heating during deep burial. Sedimentary layers of anhydrite may be interbedded with gypsum, halite and limestone. Anhydrite also occurs with other sulfates, carbonates and sulfides in hydrothermal vein and replacement ore deposits.

6.3.2 cleavable anhydrite	6.3.3 anhydrite with sulfides North Parkes NSW Australia

Anhydrite and gypsum are used in the manufacture of plaster and other building materials for construction purposes.