Gypsum, Anhydrite
In China, there is a history of calling anhydrite "calcite," and in Japan, it was historically misidentified as glass. Gypsum has low hardness and prominent cleavage, and transparent selenite was once called "Mary's glass."
Desert rose and silky luster are also attractive
Basic Information
| English Name | Gypsum, Anhydrite |
|---|---|
| Japanese Name | Sekko (Gypsum), Kosekko (Anhydrite) |
| Chemical Composition | Ca[SO4]·2H2O (Gypsum), Ca[SO4] (Anhydrite) |
| Crystal System | Monoclinic / Orthorhombic |
| Hardness | 2 (Gypsum), 3–3.5 (Anhydrite) |
| Specific Gravity | 2.52 / 2.95 |
Forms, Varieties, and Associations
- ① Selenite: Tabular to acicular twins, desert rose (selenite rose).
- ② Satin Spar: Fibrous and exhibits chatoyancy.
- ③ Alabaster: An aggregate of fine crystals.
- Varieties: Gypsum/Anhydrite cat's eye, Angelite (strontium-bearing anhydrite).
- Treatment: Vivid dyeing, resin impregnation for reinforcement.
- Similar Minerals: Alabaster and massive anhydrite look similar; identification is based on specific gravity, hardness, and hydrochloric acid reaction. Related minerals: Calcite, Celestite, Barite.