Lengenbachite on Dolomite . Main crystal size: 1.5mm. Dr. Eva Drechsler Coll. Photo Joan Rosell. All rights reserved. — Photo: Joanrok · CC BY-SA 3.0
Lengenbachite
Lengenbachite is an IMA-recognized mineral species in the sulfosalt class, with the chemical formula Ag₄Cu₂Pb₁₈As₁₂S₃₉.
It crystallizes in the triclinic crystal system. It is a member of the Cylindrite structural group.
Key properties: Mohs hardness 1.5–2; specific gravity 5.8–5.85; Brown-black streak; Metallic. Anisotropism: Weak. R1 –R2: (400) 38.9–40.0, (420) 38.5–39.8, (440) 38.2–39.4, (460) 37.6–39.0 luster.
IMA symbol Len, grandfathered status — known before the IMA’s founding, named in 1905.
Hydrothermal in origin.
It is found associated with Pyrite, sphalerite, jordanite.
The name is derived from the locality at the Lengenbach quarry, Switzerland.