Vanderheydenite, Zn6(PO4)2(SO4)(OH)4·7H2O, is a new mineral from the Block 14 Opencut, Broken Hill, New South Wales, Australia. It occurs as aggregates of colourless crystals up to 0.5 mm across in voids of a sphalerite–galena matrix and is associated with anglesite, pyromorphite, sulfur, and liversidgeite. Crystals are pseudohexagonal blades up to 0.4 mm in length, flattened on {1 0 0} and exhibiting the forms {1 0 0}, {0 1 0}, and {0 2 1}. Cleavage was not observed. The Mohs hardness is estimated to be 3. The calculated density is 3.12 g/cm3 from the empirical formula and 3.06 g/cm3 from the ideal formula. The mineral is optically biaxial (–), with α = 1.565(4), β = 1.580(4) and γ = 1.582(4). The calculated 2V is 39.8°. Chemical analysis by electron microprobe gave ZnO 55.63, CuO 0.07, FeO 0.11, MnO 0.06, P2O5 14.18, As2O5 4.33, SO3 8.71, H2O 18.31, total 101.40 wt%, with H2O content derived from the refined crystal structure. The empirical formula calculated on the basis of 23 oxygen atoms is (Zn5.99Cu0.01Fe0.01Mn0.01)Σ6.02[(PO4)1.75(AsO4)0.33]Σ2.08(SO4)0.95(OH)3.91·6.96H2O. The mineral is monoclinic, P21/n, with a = 6.2040(12), b = 19.619(4), c = 7.7821(16) Å, β = 90.67(3)°, V = 947.1(3) Å3. The five strongest lines in the X-ray powder diffraction pattern are [d(Å), (I), (hkl)]: 9.826 (57) (0 2 0), 7.296 (20) (0 1 1), 6.134 (1 0 0) (0 2 1), 3.368 (10) (0 3 2, 1 5 0), 3.069 (9) (2 1 0, 0 4 2). The crystal structure of vanderheydenite (R1 = 0.0497 for 939 reflections with Fo > 4σF) contains chains of edge-sharing ZnO6 octahedra parallel to a that are linked by edge- and corner-sharing ZnO5 trigonal bipyramids and TO4 (T = P, As) tetrahedra forming zig-zag sheets parallel to {0 1 0}. Sheets are linked by half-occupied, distorted TO4 (T = P, S) tetrahedra in the [0 1 1] direction. Interstitial channels extend parallel to the a-direction and are occupied by strongly to weakly hydrogen-bonded H2O groups.

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