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Orpiment (Photo) [abbr. Orp ]

Year of discovery: 1747 (World), 1876 (Japan)

Locality list: 42 localities of orpiment

• As₂S₃
• [As³⁺₂][S₃]^6-

• Class: Orpiment group
• Class: Sulfide
• Insoluble in: HCl
• Formed by photodissociation of Realgar with Arsenolite.

• As₂ => AsSb: Getchellite

• As => Sb: Stibnite, Metastibnite
• As => Bi: Bismuthinite
• As => Sn: Ottemannite
• As => Cr: Schreibersite
• As => Rh: Bowieite
• As => Ir: Kashinite

• S => Se: Laphamite
• S => Te: Kalgoorlieite

• AsS => Sb₂: Pääkkönenite

• Color: Orange, Yellow
• Tarnish: Dull luster
• Streak: Pale yellow
• Luster: Pearly
• Diaphaneity: Transparent

• Habit: Platy, Tabular, Short prismatic
• Aggregate: Columnar, Radial, Reniform
• Twin: {100}

• Cleavage: Perfect on {010} (1 plane), Imperfect on {100} (1 plane)
• Hardness: 1.5-2
• Density: 3.5

• System: Monoclinic
• Group: 2/m, P2₁/n
• Lattice: a=11.5, b=9.6, c=4.3, β=90.4

Etymology: Auripigment (Golden pigment) in Latin