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Proustite (Photo)

Year of discovery: 1832 (World), 1898 (Japan)

Locality list: 26 localities of proustite

• Ag₃AsS₃
• [Ag⁺₃][As³⁺][S₃]^6-

• Class: Pyrargyrite group < Ag sulfosalts < Sulfosalt class
• Class: Sulfosalt
• Soluble in: HNO₃
• Insoluble in: HCl
• Lightfastness: Turn black by Light exposure, and it can be washed off by soapy water.

• Polymorph: Xanthoconite (Low temperature, Monoclinic)

• As => Sb: Pyrargyrite (Series), Pyrostilpnite

• Color: Red
• Tarnish: Black (by light exposure)
• Streak: Red
• Luster: Adamantine
• Diaphaneity: Translucent

• Habit: Prismatic, Rhombohedral with {0112} and {1011}, Scalenohedral with {12-31}
• Twin: {1014},{1011},{0001}, and {0112}

• Cleavage: Distinct on {1011} (3 planes)
• Hardness: 2-2.5
• Density: 5.6

• System: Trigonal
• Group: (-3)m, R(-3)c
• Lattice: a=10.8, c=8.7

Etymology: Joseph Louis Proust (1754-1826), French chemist