Formula: Ag₃Bi₇S₁₂. Ag may be replaced by minor Cu and Bi by minor Pb.

Species:

Colour: Grey; tarnishes dull or yellow to copper-red

Lustre: Metallic

Hardness: 3½

Specific Gravity: 6.34

Crystal System: Monoclinic

Member of: Pavonite Homologous Series Group

Name: For Marcus Benjamin (1857-1932), American chemist, engineer, and editor of the U.S. National Museum (Smithsonian Institute).

Co-Type Localities: Silver Bear mine (Terra mines; North mine; Terra Mining and Exploration Company mine), Camsell River area, Northwest Territories, Canada. Keeley-Frontier Mine (Canadian Keeley; Frontier Mine; Keeley Mine), South Lorrain Township, Cobalt-Gowganda region, Timiskaming District, Ontario, Canada. Outlaw Mine, Round Mountain Mining District, Toquima Range, Nye County, Nevada – USA

Difficult to distinguish from pavonite; single-crystal XRD methods are necessary.