gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1986.050.355.16 Mineralogy A New Barium Uranyl Oxide Hydrate Mineral, Protasite Pagoaga M. K. 1 Appleman D. E. 2 Stewart J. M. 1 Chemistry Department, University of Maryland, College Park, Maryland 20742, USA Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA 3 1986 50 355 125 128 22 4 1985 Copyright © 1986, The Mineralogical Society 1986 Abstract

Protasite, a new barium-containing member of the uranyl oxide hydrate group, occurs as bright orange pseudo-hexagonal platelets associated with uraninite and uranophane on unidentified rock matrix from Shinkolobwe mine, Zaïre. Protasite is monoclinic, Pn with a 12.295(2), b 7.221(1), c 6.9558(8) Å, β 90.40(2)°, and V 617.50(11) Å3. The tabular pseudo-hexagonal crystals are flattened on {010}, 0.1 mm to 0.5 mm wide and up to 0.1 mm thick. They are biaxial negative, 2 V = 60–65°, β and γ 1.79–1.83, and X = b. Sector twinning is common. Microprobe analysis shows BaO 15.0, UO3 78.0, H2O(diff.) 7.0%. The structural formula is Ba[(UO2)3O3(OH)2]. 3H2O, Z = 2, and density(calc.) = 5.827(3) g cm−3. Complete crystal-structure analysis shows protasite to be the simplest model structure of the uranyl oxide hydrate group.

 Keywords protasite new mineral uranyl oxide Shinkolobwe mine Zaïre