Formula: Ag7(Sb,As)S6
Origin of name: For Paul Billingsley, American mining engineer (1887-1962), who discovered the North Lily mine and collected the type material
Crystal system: Orthorhombic
Crystal class: 23
Twinning:
Unit cell: a = ~14.82 Å, b = ~14.82 Å, c = 10.48 Å
Colour: Dark lead-gray
Diaphaneity: Opaque
Luster: Metallic
Habit: Massive; fine grained aggregates
Hardness: 2.5
Specific gravity: 5.92
Cleavage: None
Tenacity:
Streak:
Synonyms/varieties:
Comments: Believed to have occurred in a body of high-grade silver ore
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