Description and crystal structure of nyholmite, a new mineral related to hureaulite, from Broken Hill, New South Wales, Australia

作者：Elliott P^*; Turner P; Jensen P; Kolitsch U; Pring A

来源：Mineralogical Magazine, 2009, 73(5): 723-735.

DOI：10.1180/minmag.2009.073.5.723

• nyholmite
• new mineral species
• crystal structure
• cadmium oxysalt
• arsenate
• Broken Hill
• New South Wales

Nyholmite, Cd(3)Zn(2)(AsO(3)OH)(2)(AsO(4))(2)center dot 4H(2)O, from the Block 14 Opencut, Broken Hill, New South Wales, Australia, is a new Cd-Zn arsenate species, isostructural with the minerals of the hureaulite group. The mineral occurs in a quartz-garnet-arsenopyrite matrix as white globules, tufted aggregates of fibrous crystals and radiating hemispheres of thin, colourless, bladed crystals. Associated minerals are goldquarryite, lavendulan-sampleite, scorodite-strengite and gypsum. Individual crystals are up to 0.2 mm in length and 0.05 mm across. The mineral is transparent to translucent with a vitreous lustre. It is brittle with an uneven fracture and a white streak. The Mohs hardness is 3-3.5 and the calculated density is 4.23 g cm(-3) for the empirical formula. Electron microprobe analyses yielded CdO 34.58, ZnO 9.72, MnO 3.59, CuO 3.39, Al(2)O(3) 0.20, CaO 0.16, PbO 0.37, As(2)O(5) 34.55, P(2)O(5) 6.29 totalling 92.85 wt.%. The empirical formula, based on 20 oxygen atoms, is Ca(0.03)Pb(0.02) Cd(2.80)Al(0.04)Zn(1.24)Cu(0.44)Mn(0.53)[(AsO(4))(3.13)(PO(4))(0.92)](Sigma 4.05)H(1.91)center dot 3.79H(2)O. Nyholmite is monoclinic, C2/c, a = 18.062(4) angstrom, b = 9.341(2) angstrom, c = 9.844(2) angstrom, beta = 96.17(3)degrees, V = 1651.2(6) angstrom(3) (single-crystal data, at 123 K). The six strongest lines in the X-ray powder diffraction pattern are [d(angstrom),I,(hkl)]: 8.985,30,(200); 8.283,85,(110); 6.169,25,(111); 4.878,25,(002); 3.234,100,(2 (2) over bar(2) over bar, 420); 3.079,65,(222, 511); 2.976,45,(113). The crystal structure was solved by Patterson methods and refined using 2045 observed reflections to R1(F) = 3.73%. The structure is characterized by a kinked, five-membered chain of edge-sharing M phi(6) (phi = unspecified anion) octahedra, or pentamer, that extends in the a direction. The pentamers link by sharing corners to form a sheet in the (001) plane. Pentamers are also linked, via corner-sharing, by (As,P)O(4) groups forming thick slabs in the (001) plane. The slabs link in the c direction by corner-sharing between octahedra and tetrahedra to form a dense heteropolyhedral framework. Moderate to weak hydrogen-bonding provides additional linkage between the slabs.

• 出版日期2009-10