Radovanite, Cu2Fe+3(As+5O4)(As+3O2OOH)2H2O, a new mineral:: Its description and crystal structure

Radovanite, Cu2Fe+3(AS(+5) O-4)(AS(+3)O(2)OH)(2)H2O, a new mineral: its description and crystal structure. - Radovanite, Cu2Fe+3(AS(+5)O(4))(AS(+3)O(2)OH)(2)H2O, occurs at the old copper mines of Rona (Alpes-Maritimes, France), associated with cuprite, native copper, malachite, trippkeite, olivenite and algodonite. It forms aggregates (2mm in diameter) formed by small equidimensional crystals or slightly elongated crystals along a or b (0.15 x 0.08 x 0.02 mm maximum dimension). The megascopic color is green pistachio. The mineral is not twinned and has no cleavage. It is orthorhombic, Pnma, a=9.585(1), b=13.143(1), c=8.0884(7) Angstrom, V=1018.9(2) Angstrom(3), Z=4, d(meas)=3.9(1) and d(calc)=3.83(1) g/cm(3). The strongest lines in the X-ray powder diffraction pattern (d(obs) in, (hkl), Ivis) are : 6.88, (011), 25; 6.179, (101), 90; 3.241, (122), 40; 3.090, (202), 100; 2.710, (240) (321), 25; 2.214, (251) (223), 25. Mohs' hardness could not be measured because of the small grain size. Luster is vitreous transparent, streak is green; crystals are biaxial (-) with alpha =1.80(1), beta =1.84(1). gamma = 1.86(1) at 589 nm; 2V(obs) = 65(5)degrees, 2V(calc) = 70(3)degrees. It is pleochroic with gamma = green pistachio, beta = yellow green, alpha = light green to colorless. The optical orientation is a = beta, b = gamma and c = alpha. The crystal structure was solved by direct methods (MoKalpha radiation) and refined using 1027 observed unique reflections to R = 0.059, Rw = 0.023. The structure of radovanite is formed by a three-dimensional network formed by pairs of edge-sharing CuO5 square pyramids and FeO6 octahedra interconnected by AsO4 tetrahedra and ASO(3) triangles. The water molecul is fixed in a structure cavity by hydrogen bonds of its two hydrogen atoms and of the OH group which is shared between the CuO5 square pyramid and ASO(3) triangle.