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Gypsum (Photo) [abbr. Gp ]

Year of discovery: Prehistoric (World), 1890 (Japan)

Locality list: 567 localities of gypsum

• CaSO₄,2H₂O
• [Ca²⁺][SO₄]^2-,2H₂O

• Class: Sulfate - Hydrate
• Variety: Alabaster (Fine grained)
• Variety: Selenite (Clear)
• Variety: Satinspar (Fibrous)
• Soluble in: Water (Slightly), HCl
• Fluorescence: UV excitation (Green, Yellow), Phosphorescence (Bluish green)
• Formed by hydration of Glauberite releasing Na₂SO₄.
• Formed by hydration of Bassanite under humid condition.
• Substitution pseudomorph: Replaced by Bassanite.
• Incrustation pseudomorph: Replaced by Malachite.

• SO₄ => HPO₄: Brushite
• SO₄ => HAsO₄: Pharmacolite

• 2H₂O => H₂O: Anhydrite
• 2H₂O => 0.5H₂O: Bassanite

• Color: Colorless, White
• Streak: White
• Luster: Vitreous
• Diaphaneity: Transparent-Translucent

• Habit: Truncated Prismatic

• Cleavage: Perfect on {010} (1 plane), Distinct on {100} and {011} (2 planes)
• Hardness: 2
• Density: 2.3

• System: Monoclinic
• Group: 2/m, A2/a
• Lattice: a=5.7, b=15.2, c=6.5, β=118.4