LAUSR

Abstract Meyrowitzite, Ca(UO2)(CO3)2⋅5H2O, is a new mineral species from the Markey mine, Red Canyon, San Juan County, Utah, U.S.A. It is a secondary phase found on calcite-veined asphaltum in association with gypsum, markeyite, and rozenite. Meyrowitzite occurs as blades up to about 0.2 mm in length, elongate on [010], flattened on {100}, and exhibiting the forms {100}, {001}, {101}, {110}, and {011}. The mineral is yellow and transparent with vitreous luster and very pale yellow streak. Fluorescence under a 405 nm laser is from weak greenish yellow to moderate greenish blue. The Mohs hardness is ca. 2, tenacity is brittle, fracture is irregular, and there is one perfect cleavage, {101}. The measured density is 2.70(2) g/cm3. The mineral is optically biaxial (+) with α = 1.520(2), β = 1.528(2), and γ = 1.561(2) (white light). The 2V(meas) = 53.0(6)°; weak dispersion, r > ν; optical orientation: Z = b, Y ^ a = 19° in obtuse β; pleochroism pale yellow, X ≈ Y < Z. Electron microprobe analyses provided the empirical formula Ca0.94(U1.00O2)(CO3)2⋅5(H2.02O) on the basis of U = 1 and O = 13 apfu, as indicated by the crystal structure determination. Meyrowitzite is monoclinic, P21/n, a = 12.376(3), b = 16.0867(14), c = 20.1340(17) Å, β = 107.679(13)°, V = 3819.3(12) Å3, and Z = 12. The structure (R1 = 0.055 for 3559 Io > 2σI) contains both UO7 pentagonal bipyramids and UO8 hexagonal bipyramids, the latter participating in uranyl tricarbonate clusters (UTC). The two kinds of bipyramids and the carbonate groups link to form a novel corrugated heteropolyhedral sheet. This is the first structural characterization of a uranyl-carbonate mineral with a U:C ratio of 1:2. Meyrowitzite is apparently dimorphous with zellerite.