• journal_title：European Journal of Mineralogy
• Contributor：Halil SARP ; Radovan ČERNÝ
• Publisher：E. Schweizerbart'sche Verlagsbuchhandlung Science Publishers
• Date：2000-
• Format：text/html
• Language：en
• Identifier：10.1127/0935-1221/2000/0012-1045
• journal_abbrev：Eur J Mineral
• issn：0935-1221
• volume：12
• issue：5
• firstpage：1045
• section：Articles

Rollandite, Cu₃ (AsO₄)₂-4H₂O, was found in the old copper mines of Roua (Alpes-Maritimes, France), associated with olivenite, conichalcite, clinotyrolite, cornubite, kolfanite, pharmacosiderite, gerhardtite, atacamite, gilmarite, wallkilldellite-Fe, cuprite, domeykite, algodonite and native copper. It forms aggregates (1mm diameter) consisting of perfect crystals (0.5 × 0.15 × 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) ų, Z = 4, D_meas = 3.9(1) and D_calc = 3.84 g/cm³. The strongest lines in the X-ray powder diffraction pattern (d_obs in Å, (hkl), I_vis) 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 α = 1.745(5), β = 1.755(5), γ = 1.760(5) at 590 nm; 2V_obs = 71(2)°, 2V_calc = 70.1(4)°. Non pleochroic. The crystal structure was solved by direct methods (MoKα radiation) and refined using 1407 observed unique reflections to R = 0.086, R_w = 0.046. The structure of rollandite is formed by (020) sheets of CulO₆ octahedra and [100] chains of Cu2O₅ square pyramids linked by AsO₄ tetrahedra. The water molecule O6H₂ is bonded by hydrogen bonds in the channels running along [100].