Formula: (Ag,Cu,Fe)9(Se,S)8
Origin of name: For Jacques Geffroy, French metallurgist
Crystal system: Cubic
Crystal class: 4/m -3 2/m
Twinning:
Unit cell:
Colour: Brown (reflected light)
Diaphaneity: Opaque
Luster: Metallic
Habit: Intergrowth with clausthalite and eskebornite
Hardness: 4
Specific gravity: 5.39
Cleavage: None
Tenacity:
Streak:
Synonyms/varieties:
Comments:
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