Robinsonite, a new lead antimony sulphide

Crystals of robinsonite are triclinic, with probable space group PT; a:16.51,b:17.62, c:3.97A, a:96"04', 0:96"22', l:91"12'. Slender prismatic [001], striated [001]; also massive, frbrous to compact. Cleavage was not observed; fracture is irregular; brittle, H 2.5-3. Measured specific gravity: 5.27 (artificial crystals), 5.20,5.25 (natural fragments), 5.34 (artificial fused material), and 5.28 (indirect determination on natural material). Composition and cell content is TPbS 6SbzSa with calculated specific gravity 5.40. Strongest r ray powder l ines: 4.08A(6), 3.97(6),3.41(10), 3.19(6),3.04(6), 2.74(5),2.68(5). Robinsonite occurs as a primary mineral with pyrite, sphalerite, stibnite, and boulangerite in small pieces in oxidized ore bodies at the Red Bird mercury mine, Pershing County, Nevada.