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The crystal structure of cyanotrichite

Published online by Cambridge University Press:  02 January 2018

Stuart J. Mills ,
Andrew G. Christy ,
Fernando Colombo  and
Jason R. Price
Stuart J. Mills*
Affiliation:
Geosciences, Museum Victoria, GPO Box 666, Melbourne, Victoria 3001, Australia
Andrew G. Christy
Affiliation:
Centre for Advanced Microscopy and Department of Applied Mathematics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200, Australia
Fernando Colombo
Affiliation:
CICTERRA-CONICET and Cátedra de Mineralogía, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Vélez Sarsfield 1611 (X5016GCA), Córdoba, Argentina
Jason R. Price
Affiliation:
Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria 3168, Australia
*
*E-mail: smills@museum.vic.gov.au
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Abstract

We report the single-crystal average structure of cyanotrichite, Cu4Al2[SO4](OH)12(H2O)2, from the Maid of Sunshine mine, Arizona, USA. Cyanotrichite crystallizes in space group C2/m, with the unit-cell parameters a = 12.625(3), b = 2.8950(6), c = 10.153(2) Å and β = 92.17(3)o. All non-hydrogen atoms were located and refined to R1 = 0.0394 for all 584 observed reflections [Fo > 4σFo] and 0.0424 for all 622 unique reflections. The cyanotrichite structure consists of a principal building unit of a three-wide [Cu2Al(OH)6] ribbon of edge-sharing Cu and Al polyhedra || b, similar to that found for camerolaite. The ribbons lie in layers || (001) and between these layers, while SO4 tetrahedra and H2O molecules form rods running || b. A hydrogen-bonding scheme is also proposed.

A sample of cyanotrichite from the Cap Garonne mine, Le Pradet, France, showed a 4b superstructure with the following unit cell: space group P2/m, a = 12.611(2) Å, b = 11.584(16) = 4 × 2.896(4) Å, c = 10.190(1) Å and β = 92.29(6)o. The supercell could not be refined in detail, but nevertheless imposes constraints on the local structure in that while the space-group symmetry prevents full order of SO4 and H2O in the 4b supercell, it requires that the sequence of species along any given rod is [-SO4-SO4-(H2O)2-(H2O)2-] rather than [-SO4-(H2O)2-SO4-(H2O)2-].

Keywords

cyanotrichitecamerolaitecarbonatecyanotrichitekhaidarkanitemerotypesuperstructurecrystal structuresynchrotron
Type
Research Article
Information
Mineralogical Magazine , Volume 79 , Issue 2 , April 2015 , pp. 321 - 335
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2015

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