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Staurolite [abbr. St ]

Year of discovery: 1792 (World), 1899 (Japan)

Locality list: 61 localities of staurolite

• Fe_1.5Al₉Si₄O₂₂(OH)₂
• (Fe,Mg,Zn)_1.5-2Al₉(Si,Al)₄O₂₂(O,OH)₂
• [Fe²⁺_1.5][Al³⁺₉][O₆|(OH)₂|(SiO₄)₄]^24-

• Class: Nesosilicate - Oxide - Hydroxide
• Insoluble in: HCl
• Substitution pseudomorph: Replaced by Biotite.

• Fe => Mg: Magnesiostaurolite
• Fe => Zn: Zincostaurolite

• Color: Dark brown, Reddish brown
• Streak: Gray
• Luster: Vitreous
• Diaphaneity: Translucent

• Habit: Prismatic
• Aggregate: Crossed twin
• Twin: Intrusive Twin

• Cleavage: Distinct on {010} (1 plane)
• Hardness: 7-7.5
• Density: 3.8

• System: Monoclinic
• Group: 2/m, C2/m
• Lattice: a=7.9, b=16.6, c=5.7, β=90.5

Etymology: Stauros (Cross) in Greek