Kunatite, CuFe_2(PO_4)_2(OH)_2 centre dot 4H_2O, a new member of the whitmoreite group, from Lake Boga, Victoria, Australia

摘要

Kunatite, CuFe_2(PO_4)_2(OH)_2 centre dot 4H_2O, (IMA 2007-057), is a newly defined mineral from a quarry in Late Devonian granite near Lake Boga, northern Victoria, Australia. The mineral occurs as acicular to lath-like micro crystals forming compact to slightly open spheres, hemispheres and flattened sprays up to about 0.25 mm across, with individual fibrous crystals up to 30 mu m long and 5 mu m thick. Kunatite is associated only with chalcosiderite-turquoise. The crystals are yellow-green with a pale yellow streak and are transparent; the lustre of the aggregates is silky and the estimated Mohs hardness is 3. Kunatite is monoclinic, P2_1/c, with a = 9.863(10), b = 9.661(6), c = 5.476(6) A, beta = 92.45(3) deg, V = 521.3(3) A~3 and Z = 2. The calculated density, based on the empirical formula, is 3.063 g/cm~3. Crystals are biaxial (-), with alpha = 1.703(3), beta = 1.742(4) and gamma = 1.762(3), and 2V_(calc) = 70 deg. Orientation: Z approx c, with straight extinction and slight pleochroism: X = very pale yellow (almost colourless), gamma = pale yellowish, Z = yellowish. The strongest five powder-diffraction lines [d in A, (I/I_0), (hkl)] are: 9.849, (100), (100); 4.386, (90), (210); 6.892, (80), (110); 4.924, (80), (200); 2.697, (60), (320,002,230). Kunatite is a new member of the whitmoreite group and the phosphate-dominant analogue of arthurite. The name is derived from the Australian aboriginal words kunat kunat, meaning cotton weed (sp. Actinobole uliginosum). Kunatite also occurs at the Huber open pit, near Krdsno in the Czech Republic. Raman spectra of both type and Czech kunatite and infrared spectra of the Czech kunatite are also presented.