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Birchite, a new mineral from Broken Hill, New South Wales, Australia: Description and structure refinement

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Veröffentlicht/Copyright: 1. April 2015
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American Mineralogist
Aus der Zeitschrift American Mineralogist Band 93 Heft 5-6

Abstract

The new mineral species birchite, idealized formula Cd2Cu2(PO4)2(SO4)·5H2O, occurs on specimens from the Block 14 Opencut, Broken Hill, New South Wales, Australia, as sprays and aggregates of crystals to 0.75 mm across on a host rock composed of quartz, garnet, galena, chalcopyrite, and fluorapatite. It is a late-stage supergene mineral formed as part of a suite of secondary phosphate minerals under low-temperature conditions. Associated secondary minerals are covellite, cerussite, anglesite, plumbogummite-hinsdalite, pyromorphite, libethenite, and sampleite. Individual crystals are bladed to prismatic and acicular in habit, with a maximum length of 0.3 mm and width of 0.05 mm. The crystals are elongated along [001] and sometimes also flattened on (100). The crystal forms are major {100} and {010}, and minor {101} and {001}. Birchite is orthorhombic, space group Pnma, with unit-cell parameters refined from powder X-ray diffraction data, a = 10.489(6), b = 20.901(7), c = 6.155(5) Å, V = 1349.6(3) Å3, and Z = 4. The eight strongest lines in the diffraction pattern are [d(Å)(I)(hkl)]: 10.451(100)(020); 5.146(28)(111); 4.223(38)(131); 3.484(39)(060); 2.902(70)(260); 2.719(33)(132); 2.652(32)(042); 1.919(80)(432). Birchite is translucent (masses) to transparent (crystals); pale blue with a vitreous luster. Optically, birchite is biaxial positive, with nα = 1.624(4), nβ = 1.636(5), nγ = 1.669(4), and 2Vcalc = +63°. The optical orientation is X = b, Y = a, Z = c; the optical axis plane lies within the {100} plane. Birchite shows very faint pleochroism, X = pale bluish, Z = pale greenish, absorption Z ≥ X. Birchite is brittle, has a conchoidal fracture and is nonfluorescent. Hardness (Mohs) is 3.5-4; the measured density is 3.61(4) g/cm3, and the calculated density is 3.647 g/cm3 (from the empirical formula). Average electron microprobe analysis (wt%): CdO 36.79, CuO 21.22, CaO 0.17, MnO 0.17, ZnO 1.07, P2O5 20.21, SO3 9.70, H2O (from crystal-structure analysis) 12.37, total 101.70. The empirical formula, calculated on the basis of 17 O atoms and with H2O calculated to give 5H2O is (Cu1.94,Zn0.10)Σ2.04(Cd2.09,Ca0.02,Mn0.02)Σ2.13P2.07S0.88O12·5H2O. The crystal structure has been refined to an R index of 4.3% for 846 observed reflections measured with MoKα X-radiation. Alternating [CdO4(H2O)2] octahedra and [CuO3(H2O)2] square-pyramids share edges to form chains that extend along the a axis, which are linked by (PO4) tetrahedra to form [CdCu(PO4)(H2O)2O] sheets in the (010) plane. Two such sheets are linked via (PO4) tetrahedra vertices to form a layer in the (010) plane. Two layers, which are related by mirror symmetry, are linked via (SO4) tetrahedra vertices to form a heteropolyhedral framework structure. Interstitial channels within the framework extend along both the a and c axes and are occupied by a H2O group. The mineral is named for William D. Birch, Senior Curator of Geosciences at Museum Victoria, Australia.

Keywords: Birchite; new mineral species; crystal structure; cadmium oxysalt; phosphate; sulfate; Broken Hill; New South Wales
Received: 2007-7-5
Accepted: 2007-12-26
Published Online: 2015-4-1
Published in Print: 2008-5-1

© 2015 by Walter de Gruyter Berlin/Boston

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https://doi.org/10.2138/am.2008.2732
Schlagwörter für diesen Artikel
Birchite; new mineral species; crystal structure; cadmium oxysalt; phosphate; sulfate; Broken Hill; New South Wales

Artikel in diesem Heft

  1. The crystal structure of vurroite, Pb20Sn2(Bi,As)22S54Cl6: OD-character, polytypism, twinning, and modular description
  2. Mineralogy of the Paso Robles soils on Mars
  3. Dingdaohengite-(Ce) from the Bayan Obo REE-Nb-Fe Mine, China: Both a true polymorph of perrierite-(Ce) and a titanic analog at the C1 site of chevkinite subgroup
  4. Thermal equation of state of CaGeO3 perovskite
  5. Quantitative absorbance spectroscopy with unpolarized light: Part I. Physical and mathematical development
  6. Quantitative absorbance spectroscopy with unpolarized light: Part II. Experimental evaluation and development of a protocol for quantitative analysis of mineral IR spectra
  7. Oxide-melt solution calorimetry of selenides: Enthalpy of formation of zinc, cadmium, and lead selenide
  8. Precise dating of biotite in distal volcanic ash: Isolating subtle alteration using 40Ar/39Ar laser incremental heating and electron microprobe techniques
  9. Rationale for the existence of four- and eight-reversals in antigorite
  10. Structural relaxation around substitutional Cr3+ in pyrope garnet
  11. Metasomatic thorite and uraninite inclusions in xenotime and monazite from granitic pegmatites, Hidra anorthosite massif, southwestern Norway: Mechanics and fluid chemistry
  12. Interlayer potassium and its neighboring atoms in micas: Crystal-chemical modeling and XANES spectroscopy
  13. Effect of chemical environment on the hydrogen-related defect chemistry in wadsleyite
  14. Fracture toughness, hardness, and elastic modulus of kyanite investigated by a depth-sensing indentation technique
  15. Crystal chemistry of the natrojarosite-jarosite and natrojarosite-hydronium jarosite solid-solution series: A synthetic study with full Fe site occupancy
  16. A new experimental thin film approach to study mobility and partitioning of elements in grain boundaries: Fe-Mg exchange between olivines mediated by transport through an inert grain boundary
  17. Titanium as a cathodoluminescence activator in alkali feldspars
  18. Biogenic vs. abiogenic magnetite nanoparticles: A XMCD study
  19. Solubility of andradite, Ca3Fe2Si3O12, in a 10 mol% NaCl solution at 800 °C and 10 kbar: Implications for the metasomatic origin of grandite garnet in calc-silicate granulites
  20. A 3D reconstruction of plagioclase crystals in a synthetic basalt
  21. Rudashevskyite, the Fe-dominant analogue of sphalerite, a new mineral: Description and crystal structure
  22. Birchite, a new mineral from Broken Hill, New South Wales, Australia: Description and structure refinement
  23. Crystal structure of synthetic Al4B2O9: A member of the mullite family closely related to boralsilite
  24. Interaction of gypsum with As(V)-bearing aqueous solutions: Surface precipitation of guerinite, sainfeldite, and Ca2NaH(AsO4)2·6H2O, a synthetic arsenate
  25. Jahnsite-(NaFeMg), a new mineral from the Tip Top mine, Custer County, South Dakota: Description and crystal structure
  26. Evidence for anomalously large degree of polymerization in Mg2SiO4 glass and melt
  27. Theoretical infrared absorption coefficient of OH groups in minerals
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