Fletcherite, Cu(Ni, Co) 2 S 4 , a new thiospinel mineral, occurs in copper-rich pods in the Fletcher mine of the Viburnum Trend (New Lead Belt) of southeast Missouri. Fletcherite occurs as euhedral to subhedral crystals 5 to 200 mu m in diameter, disseminated in pods of bornite, chalcopyrite, and digenite. Other associated minerals include covellite, pyrite, vaesite, galena, and tetrahedrite. Reflected light examination reveals that fletcherite takes a good polish, is creamy white, has a moderate reflectivity, is isotropic, and has a polishing hardness between chalcopyrite and pyrite. Micro-indentation hardness measurements yield VHN values of 368 to 464 kg/mm 2 . Measured reflectivities, R% (at specific wavelengths) are: 36.4 (420 nm), 40.9 (460 nm), 42.5 (500 nm), 43.4 (546 nm), 45.3 (589 nm), 43.8 (600 nm).The compositional range observed among 39 individual analysis is Cu (sub 1.13) Ni (sub 1.04) Co (sub 0.84) Fe (sub 0.06) S (sub 4.00) to Cu (sub 0.67) Ni (sub 2.11) Co (sub 0.61) Fe (sub 0.01) S (sub 4.00) . The Space Group is Fd3m, Z = 8, a o = 9.520Aa. The name is for the Fletcher mine of the St. Joe Minerals Corporation in which the type material was found.

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