La vanmeersscheite U(UO2)3(PO4)2(OH)6 • 4 H2O et la méta-vanmeersscheite U(UO2)3(PO4)2(OH)6 • 2 H2O, nouveaux minéraux

Abstract

Vanmeersscheite (VM) and meta-vanmeersscheite (mVM) occur as canary yellow tablets. Optically for VM : 2V(-) = 56°, np = 1.704, nm = 1.715, ng = 1.718, and for mVM : 2 V(-) = 83°, np = 1.67, nm = 1.68 et ng = 1.69. Orthorhombic system with, for VM : a = 17.06, b = 16.76, c = 7.023 Å, Z = 4, space group P2₁mn, and for mVM : a = 34.18, b = 33.88, c = 14.074 Å, Z = 32, space group Fddd. Chemical analysis by electron microprobe : VM : UO₃ 80.76, P₂O₅ 10.40, H₂O 8.84 ; mVM : UO₃ 83.24, P₂O₅ 10.20, H₂O 6.56. The crystal structure of VM has been determined by X-ray diffraction (R = 12.6 %). Structure type : phosphuranylite. Both minerals occur at Kobokobo (Kivu, Zaïre). Names are in honor of the Belgian crystallographer Maurice Van Meerssche.