Rameauite and agrinierite, two new hydrated complex uranyl oxides from Margnac, France

Abstract

SummaryTwo new hydrated uranyl oxides from Margnac, France, are described. Rameauite, K2O.CaO.6UO3.9H2O, occurs with uranophane and calcite on pitchblende, agrinierite, 2(K2O, CaO,SrO). 6UO3.8H2O, with uranophane in small cavities in ‘gummite’.Rameauite is monoclinic with a 13·97, b 14·26, c 14·22 Å, β 121° 1′±5′; the space group is C2/c. The principal d-spacings, with hkl values and relative intensities, are: 7·12, 020, vvs; 3·566, 040, vs; 3·495, 40, vvs; 3·473, 202, vs; 3·185, 22, vs; 3·139, 42, vvs; 2·993, 400, vvs; 2·495, 44, ms. Measured density 5·6 g.cm−3. The orange crystals are twinned on {100}, flattened on {010} and elongate parallel to [001]; there is a good {010} cleavage. α ‖; [010], γ: [001] 4 to 6° in the obtuse angle β, 2Vα 32°; the two principal reflectivities for yellow light on {010} are 10·6 and 10·4%. The main endothermic peaks on the d.t.a. diagram are at 95, 130, and 170 °C (loss of water), and at 1050 °C (loss of oxygen).Agrinierite is orthorhombic with a 14·04, b 24·07, c 14·13 Å; space group Cmmm on the assumption of holohedral symmetry. Measured density 5·7 g.cm−3. The principal d-spacings are 7·08, 002, vvs; 6·05, 220, ms; 3·516, 400 & 332, s; 3·485, 062 & 260, vs; 3·153, 204 & 134, vs; 3·128, 262, vvs; 2·023, 660, s. The orange crystals are tabular on {001} with pseudo-hexagonal section bounded by the trace of (010), and show sector twinning on {110} as in billietite; there is a good {001} cleavage. The two reflectivities for yellow light on the face (001) are 12·0 and 11·2 %, corresponding to a refractive index of about 2. α ‖ [001], γ ‖ [010], 2Vα 55°. The principal endothermic d.t.a. peaks are at 163 °C (loss of water) and 1060 °C (loss of oxygen).Rameauite is named after J. Rameau and agrinierite after H. Agrinier. The original specimens are deposited in the Mineralogical Collection of the University of Paris VI.