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(mineralogy) An uncommon silver germanium sulfide mineral, black with a purplish tinge and metallic lustre.

Sulfide mineral – Ag₈GeS₆ – Agy – 2.BA.35 – Orthorhombic – Pyramidal (mm2) – H-M symbol: (mm2) – Pna2₁ – A = 15.149, b = 7.476 – C = 10.589 [Å]; Z = 4 – Black, purplish tinge – Pseudo-octahedra or pseudo-cubic, dodecahedra, cubes; radiating crystal aggregates, botryoidal crusts, or massive – Pseudospinel law {111} penetration twins – Absent – Uneven to conchoidal – 2.5 – Metallic – Opaque – 6.2-6.5 – Weakly anisotropic – Weak.