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Chalcocite (Photo) [abbr. Cct ]

Year of discovery: 1832 (World), 1891 (Japan)

Locality list: 317 localities of chalcocite

• Cu₂S
• [Cu⁺₂][S]^2-

• Class: Chalcocite group
• Class: Sulfide
• Soluble in: HNO₃
• Insoluble in: HCl
• Substitution pseudomorph: Replace Galena. (Harrisite)

• Cu => Ag: Argentite, Acanthite

• Cu₂ => Cu_1.2: Yarrowite (Series)
• Cu₂ => AgCu: Stromeyerite

• Cu_1.5 => Ag_1.5: Jalpaite

• Cu_1.75 => Ag_1.75: Mckinstryite

• Color: Lead gray
• Tarnish: Blue
• Streak: Dark gray
• Luster: Metallic
• Diaphaneity: Opaque

• Habit: Short prismatic elongated to [001], Thick tabular parallel to {001}, Long prismatic elongated to [100]
• Striation: [100] on {001}
• Twin: {110} Common, {032}{112} reported.

• Cleavage: Indistinct on {110} (1 plane)
• Hardness: 2.5-3
• Density: 5.7

• System: Monoclinic, Pseudotetragonal
• Group: 2/m, P2₁/c
• Lattice: a=15.2, b=11.9, c=13.5, β=116.4

Etymology: Chalkos (Copper) in Greek