Original paper

Rollandite, Cu3 (AsO4)2.4H2O, a new mineral: its description and crystal structure

Sarp, Halil; Černý, Radovan

European Journal of Mineralogy Volume 12 Number 5 (2000), p. 1045 - 1050

18 references

published: Oct 4, 2000
manuscript accepted: May 10, 2000
manuscript received: Mar 6, 2000

DOI: 10.1127/0935-1221/2000/0012-1045

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ArtNo. ESP147051205011, Price: 29.00 €

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Abstract

Abstract Rollandite, Cu3 (AsO4)2 .4H20. was found in the old copper mines of Roua (Alpes-Maritimes, France), associated with olivenite, conichalcite. clinotyrolite, comubite, kolfanite, pharmacosiderite, gerhardtite, atacamite. gilmarite, wallkilldellite-Fe, cuprite, domeykite, algodonite and native copper. It forms aggregates (lmm diameter) consisting of perfect crystals (0.5 x 0.15 x 0.1 mm maximum dimension). The bottle-green crystals are elongated along a, slightly flattened on {010}. and have a good cleavage on {001}. They are not twinned. The mineral is orthorhombic, Pnma, a = 5.6906(4), b = 17.061(1), c = 9.732(1) Å, V = 944.9(1) Å3, Z = 4, Dmea3= 3.9(1) and Dcalc = 3.84 g/cm3. The strongest lines in the X-ray powder diffraction pattern (dobs in Å. (hkl). Zvis) are: 8.52, (020). 100; 3.721, (131), 60; 3.221, (141) (051), 90; 3.102, (132), 40; 2.817, (103)(033), 35; 2.795, (142), 35; 2.350, (143) (053), 25; 2.133. (080) (251), 25. Mohs’ hardness is 4-4.5. Luster is vitreous transparent, streak is very light green; crystals are biaxial (-) with a = 1.745(5). p = 1.755(5), y = 1.760(5) at 590 nin; 2Vobs = 71(2)°, 2Vcalc = 70.1(4)°. Non pleochroic. The crystal structure was solved by direct methods (MoKa radiation) and refined using 1407 observed unique reflections to R = 0.086, Rw = 0.046. The structure of rollandite is formed by (020) sheets of CulOg octahe- dra and [100] chains of Cu2O5 square pyramids linked by AsO4 tetrahedra. The water molecule 06H2 is bonded by hydrogen bonds in the channels running along [100].

Keywords

rollanditenew mineralpowder patterncrystal structurearsenatecopperhydrogen bonding