Les phosphates d'uranyle et d'aluminium de Kobokobo. II. La phuralumite Al2 (UO2)3 (PO4)2 (OH)6 • 10H2O et l'upalite Al (UO2)3 (PO4)2 (OH)3, nouveaux minéraux

Abstract

Phuralumite occurs as yellow lemon prismatic crystals. Perfect vertical cleavage {010}. Maximum length 1/2 mm. Density (measured) 3.5 g/cm3. Optically biaxial negative, 2V = 40° ; ng (pale yellow) = 1.624, nm (pale yellow) = 1.616 and np (bright yellow) = 1.559. Phuralumite is monoclinic, P21/a with a = 13.87 Å, b = 20.79 Å, c = 9.38 Å and β = 112° ; Z = 4 ; d(calc) = 3.54 g/cm3. The strongest lines of the X-ray powder pattern are : 10.4 Å (100) 020, 3.08 Å (80) 202-213-422, 5.17 Å (70) 040 and 3.40 Å (50) 242. Formula deduced from electron microprobe analysis (H2O by difference) : Al2 (UO2)3(PO4)2(OH)6-10H2O. Upalite occurs as acicular prisms. Colour : amber yellow, transparent. Maximum length : 1/3 mm. Cleavage {010} distinct. Density (measured) 3.5 g/cm3. The mineral is orthorhombic ; space group Bbcm or Bba2 with a = 34.68 Å , b = 16.81 Å and c = 13.72 Å. Z = 16. Calculated density 3.58 g/cm3. The strongest lines of the X-ray powder pattern are : 8.4 Å (100) 020, 4.18 Å (80) 040, 3.43 Å (80) 004 and 2.903 Å (75) 10.2.2. Upalite is biaxial, 2 V(—) = 74° ; ng (canary yellow) = 1.676, nm (canary yellow) = 1.666 and np (colourless) = 1.649. Formula from microprobe analysis (H2O by difference) : Al (UO2)3 (OP4)2 (OH)3. Structural group of phosphuranylite, as well as phuralumite. Both minerals occur at Kobokobo, Kivu, Zaïre, as crystalline crusts and veinlets on pegmatitic rocks. The names after the chemical composition.