Grandviewite, Cu3Al9(SO4)2(OH)29, a new mineral from the Grandview mine, Arizona, USA

Grandviewite, Cu3Al9(SO4)2(OH)29, (IMA 2007-004), is a new mineral from the Grandview mine, Grand Canyon, Arizona, USA. The name is given for the locality. The mineral forms radiating sprays of extremely acicular laths, up to 0.5 mm in length and about 2 μm thick. Individual crystals are of the order of 0.1 μm thick. Laths are elongated parallel to [100] or [001] and flattened on {001} or {100}. Grandviewite is most frequently perched on botryoidal crusts of chalcoalumite, which in turn lies on masses of cyanotrichite intermixed with minor carbonatecyanotrichite. The mineral is monoclinic, space group P2, P21, Pm, P2/m or P21/m, with a= 10.908(2), b = 6.393(3), c = 10.118(2) Å, ß = 107.47(2)˚, V = 673.0(1) Å3, Z = 1, Dcalc = 2.72 g cm-3• The ten strongest lines in the X-ray powder diffraction pattern [d in Å(I)(hkl)] are 6.208(100)(101), 3.949(79)(102), 5.287(35)(20-1)), 9.667(33)(001), 2.816(14)(30-3), 3.625(10)(30-1), 2.990 (9)(12-1), 2.413(9)(004), 2.721(8)(220), 2.019(8)(20-5, 420). Analyses of Cu (AAS), Al (colorimetric), S03 and H2O (TGA) gave CuO, 21.4; Al2O3 , 40.7; SO3, 14.5, H2O, 23.3, total 99.9 wt%. The empirical formula (based on two sulfate ions pfu) is: Cu2 .97Al8.82(SO4)2(OH)28.55• The simplified formula is Cu3Al9(SO4)2(OH)29, which requires CuO, 21.33; Al2O3 , 41.01; SO3, 14.31, H2O, 23.35 wt%. Color is greenish blue with a very pale blue streak; luster is vitreous; Mohs' hardness is 2 and the mineral is sectile. Cleavage is perfect on {100} or {001}. Grandviewite is biaxial (-), with a = 1.590(4), ß = 1.625(4), y = 1.645(4) (white light), 2V (calc.) = 72(3)˚. Pleochroism is distinct, Z =pale blue-green, Y = very pale yellow, X = very pale yellow, and is strong when concordant stacks of elongated plates are viewed perpendicular to the stacking direction.