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Ettringite

Year of discovery: 1874 (Ettringer Feld, Bellerberg volcano, Germany, and Mayener Feld, Bellerberg volcano, Germaly), 1986 (Japan)

Locality list: 2 localities of ettringite

• Ca₆Al₂(SO₄)₃(OH)₁₂,26H₂O
• [Ca²⁺₆][Al³⁺₂][(OH)₁₂|(SO₄)₃]^18-,26H₂O

• Class: Sulfate - Hydroxide - Hydrate
• Soluble in: Water (partially decompose), HCl, HNO₃, H₂SO₄
• Deliquescent
• Included in concrete of building material.

• Al => Cr: Bentorite

• Color: Colorless
• Tarnish: White (by hydration)
• Streak: White
• Luster: Vitreous
• Diaphaneity: Transparent

• Cleavage: Perfect on {1100} (3 planes)
• Hardness: 2-2.5
• Density: 1.8

• System: Trigonal
• Group: 3m, P31c
• Lattice: a=11.2, c=21.4