Eddavidite, Cu12Pb2O15Br2, a New Mineral Species, and Its Solid Solution with Murdochite, Cu12Pb2O15Cl2
2024
Melli Rosenblatt | Marcus J. Origlieri | Richard Graeme | Richard Graeme | Douglas Graeme | Robert T. Downs
Eddavidite is a new mineral species (IMA2018-010) with ideal formula, Cu12Pb2O15Br2, and cubic Fm3¯:m symmetry: a = 9.2407(9) Å:: V = 789.1(2) Å:3: Z = 2. Eddavidite is the bromine analog of murdochite, Cu12Pb2O15Cl2, with which it forms a solid solution series. The type locality is the Southwest mine, Bisbee, Cochise County, Arizona, U.S.A. Eddavidite also occurs in the Ojuela mine, Mapimí:, Durango, Mexico. Eddavidite occurs as domains within mixed murdochite&ndash:eddavidite crystals. The empirical formula, normalized to 12 Cu apfu, is Cu12(Pb1.92Fe0.06Si0.06)(O15.08F0.02)-(Br0.99Cl0.89☐:0.12). Type locality samples contain up to 67% eddavidite component, while Ojuela mine samples contain up to 62%. Mixed eddavidite&ndash:murdochite crystals show forms {100} and {111}: the habit grades from cubic through cuboctahedral to octahedral. Mixed eddavidite&ndash:-murdochite crystals exhibit good cleavage on {111}. Eddavidite is black, opaque with submetallic luster, and visually indistinguishable from intergrown murdochite. Its Mohs hardness is 4: dmeas. = 6.33 g/cm3, dcalc. = 6.45 g/cm3. The crystal structure, refined to R = 0.0112, consists of corner-sharing square planar CuO4 units, arranged in Cu12O24 metal oxide clusters, which encapsulate Br atoms. PbO8 cubes share edges with Cu12O24 clusters in a continuous framework. Eddavidite incorporates bromine remaining after desiccation of paleo-seawater at its two known localities, which were both once situated along the Western Interior Seaway.
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