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Tetradymite

Year of discovery: 1831 (Župkov, Slovakia), 1933 (Japan)

Locality list: 29 localities of tetradymite

• Bi₂Te₂S
• [Bi³⁺₂][S|Te₂]^6-

• Class: Tetradymite group
• Class: Telluride - Sulfide
• Soluble in: HCl
• Electrical: Pyroelectric

• S => Te: Tellurobismuthite
• S => Se: Kawazulite

• Te => S: Bismuthinite

• Te₂S => Se₂Te: Skippenite
• Te₂S => Se₃: Paraguanajuatite, Guanajuatite

• Color: Dark gray, Silver white
• Tarnish: Iridescent
• Streak: Dark gray
• Luster: Metallic
• Diaphaneity: Opaque

• Habit: Hexagonal pyramidal, granular, foliaged, bladed
• Twin: {01-18} fourlings, {01-15}

• Cleavage: Perfect on {0001} (1 plane)
• Hardness: 1.5-2
• Density: 7.6

• System: Trigonal
• Group: (-3)m, R(-3)m
• Lattice: a=4.2, c=29.6

Etymology: Tetradym (Fourfold) in Greek