Abstract
Compounds having the formula A(UO2)2(AsO4)2 · 8H2O, where A=Ca, H2, Na2, or (NH4)2, have been synthesized, the last two by base exchange with hydrogen-uranospinite, H2(UO2)2(AsO4)28H2O. Synthetic calcium-uranospinite and hydrogen-uranospinite crystals are thin tablets flattened on {001} with {010} and {110}. X-ray single crystal study by the Weissenberg method indicated tetragonal symmetry and gave the space group P4/nmm, if holohedral symmetry is assumed. Calcium-uranospinite has cell dimensions a0 7.19 Å, c0 8.81 (a0:c0= 1:1.225). Specific gravity 3.65 (calc.). Color lemon yellow. Perfect cleavage {001}. Optically anomalously biaxial negative (−) with α 1.591 (nearly colorless), β 1.619 (pale lemon yellow), γ 1.621 (pale lemon yellow); 2V variable, 0°-5°; r>v, moderate. Hydrogen-uranospinite has cell dimensions a0 7.16 Å, c0 8.80 (a0:c0 = 1:1.230). Specific gravity 3.55 (meas.), 3.55 (calc.). Color lemon yellow. Perfect cleavage {001}. Optically uniaxial negative (−) with ω 1.612 (pale lemon yellow), ε 1.584 (nearly colorless), Sodium-uranospinite has cell dimensions a0 7.12 Å, c0 8.70 (a0:c0=1:1-222), obtained by the powder method. Specific gravity 3.80 (calc.). Optically uniaxial negative (−) with ω 1.617 (pale yellow), ε 1.586 (colorless). Ammonium-uranospinite has cell dimensions a0 7.21 Å, c0 8.85 (a0:c0= 1:1.227), obtained by the powder method. Specific gravity 3.60 (calc.). Optically uniaxial negative (−) with ω 1.611 (pale yellow), ε 1.601 (colorless). All fluoresce bright lemon yellow in long-wave ultraviolet light and less brightly in shortwave ultraviolet light. Natural troegerite, supposedly (UO2)3(AsO4)2·12H2O, is a member of the metatorbernite group and probably has the composition H2(UO2)2(AsO4)2 · 8H2O.
