Summary: Two 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, 402¯, vvs; 3·473, 202, vs; 3·185, 224¯, vs; 3·139, 422¯, vvs; 2·993, 400, vvs; 2·495, 442¯, 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, 2V_α 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], 2V_α 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.