Description de la ludjibaïte, un polymorphe de la pseudomalachite, Cu5(PO4)2(OH)4

Abstract

Ludjibaïte occurs on red micaceous shale at Ludjiba, Zaire, in association with pseudomalachite and libethenite. It forms crest-like aggregates of small blue-green blades (up to 0.3 mm) on the surface of deep green crystals of pseudomalachite. Triclinic, space group PI, a = 4.446(3), b = 5.871(4), c = 8.680(7) Å, α = 103.9(2), β = 90.3(2), γ = 93.2(2)°, V = 219.5(3) Å3, Z = 1. Calculated density : 4.36 g.cm-3. Strongest lines of X-ray powder pattern [d(Å) (I) hkl] : 4.46(10)100, 2.462(5)1-20, 2.353(5)103 and 11-3, 3.02(2)102 and 2.408(2)-103. Biaxial positive or negative, 2V large, α' = 1.786(2) and γ' = 1.840(5). Chemical composition : CuO 69.1, P2O5 24.6, H2O 6.3 %. The corresponding artificial compound had been prepared by Shoemaker et al. (1981) who had also determined the crystal structure.