Eddavidite, Cu 12 Pb 2 O 15 Br 2 , a New Mineral Species, and Its Solid Solution with Murdochite, Cu 12 Pb 2 O 15 Cl 2.

Eddavidite is a new mineral species (IMA2018-010) with ideal formula, Cu₁₂Pb₂O₁₅Br₂, and cubic Fm 3 ¯ m symmetry: a = 9.2407(9) Å; V = 789.1(2) ų; 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–eddavidite crystals. The empirical formula, normalized to 12 Cu apfu, is Cu₁₂(Pb_1.92Fe_0.06Si_0.06)(O_15.08F_0.02)-(Br_0.99Cl_0.89☐_0.12). Type locality samples contain up to 67% eddavidite component, while Ojuela mine samples contain up to 62%. Mixed eddavidite–murdochite crystals show forms {100} and {111}; the habit grades from cubic through cuboctahedral to octahedral. Mixed eddavidite–-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; d_meas. = 6.33 g/cm³, d_calc. = 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. [ABSTRACT FROM AUTHOR]