OSWALDPEETERSITE, (UO2)2CO3(OH)2{middle dot}4H2O, A NEW BASIC URANYL CARBONATE MINERAL FROM THE JOMAC URANIUM MINE, SAN JUAN COUNTY, UTAH, U.S.A.

Abstract

Oswaldpeetersite, ideally (UO 2 ) 2 CO 3 (OH) 2 ·4H 2 O, is a newly discovered hydrated basic uranyl carbonate mineral found in the Jomac uranium mine, Brown’s Rim, San Juan County, Utah, U.S.A. It occurs along some bedding planes of a layer of siltstone within the Triassic Shinarump conglomerate. Associated minerals are gypsum, cuprite, antlerite, goethite, lepidocrocite, mbobomkulite, hydrombobomkulite, sklodowskite and two undefined uranium minerals. Oswaldpeetersite occurs as micrometric prismatic crystals (approximately 0.1 × 1 × 02 mm). These are canary yellow and transparent, with a vitreous luster and pale yellow streak. It does not fluoresce in ultraviolet radiation. The H Mohs is in the range 2–3. D meas > 4.10 g/cm 3 , D calc = 4.54 g/cm 3 (empirical formula), 4.50 g/cm 3 (idealized formula). Optically biaxial negative, α 1.583(2), β 1.669(2), γ 1.712(2), and 2 V calc = 67.4(2)°. Orientation Z || a and elongation positive. The pleochroism is X and Y very pale yellow to colorless, and Z pale yellow. The cleavage and parting are along the elongation. The tenacity is weak, and the fracture, uneven. The habit can be described as acicular. Oswaldpeetersite is monoclinic, P 2 1 / c , with unit-cell parameters refined from powder data: a 4.1425(6), b 14.098(3), c 18.374(5) A, β 103.62(1)°, V 1042.8(3) A 3 , a:b:c = 0.2938:1:1.3033 and Z = 4. The forms recognized are {100}, {010} and {001}. The strongest eight reflections of the X-ray powder pattern [ d (in A)( I )( hkl )] are: 8.95(65)(002), 7.54(63)(012), 4.55(96)(031), 4.26(60)(014), 3.46(62)(015), 3.32(100)(114), 3.029(85)(043) and 2.273(62)(062). Electron-microprobe and thermogravimetric analyses gave UO 3 81.47 and H 2 O 12.30 wt.%. The CO 2 content was calculated as 6.23 wt.% by difference. The oxide formula is 2.03 UO 3 ·1.01 CO 2 ·4.88 H 2 O, and the empirical formula is (UO 2 ) 2.03 (CO 3 ) 1.01 (OH) 2.05 ·3.85 H 2 O. The name honors the Belgian structural crystallographer Maurice Oswald Peeters, University of Leuven, Belgium.