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Dehydration phase transitions in new aluminium arsenate minerals from the Penberthy Croft mine, Cornwall, UK

Published online by Cambridge University Press:  02 January 2018

Ian E. Grey ,
Helen E. A. Brand  and
John Betterton
Ian E. Grey*
Affiliation:
CSIRO Mineral Resources, Private bag 10, Clayton South, Victoria 3169, Australia
Helen E. A. Brand
Affiliation:
Australian Synchrotron, 800 Blackburn Rd, Clayton, VIC 3168, Australia
John Betterton
Affiliation:
Haslemere Educational Museum, 78 High Street, Haslemere, Surrey GU27 2LA, UK
*
*E-mail: ian.grey@csiro.au
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Abstract

Bettertonite, [Al6(AsO4)3(OH)9(H2O)5]•11H2O and penberthycroftite, [Al6(AsO4)3(OH)9(H2O)5].8H2O, two new minerals from the Penberthy Croft mine, Cornwall, have flexible layer structures based on corner-connected heteropolyhedral columns. Their response to dehydration on heating was studied using in situ synchrotron powder X-ray diffraction at temperatures in the range -53 to 157°C. The bettertonite sample transforms to penberthycroftite in a narrow temperature range of 67 to 97°C with a large (8%) contraction of the layer separation and a 6 Å sliding of adjacent layers relative to each other. Above 100°C a second phase transition occurs to a DL (displaced layer) phase, involving another 8% inter-layer contraction combined with a rotation of the columns. On heating the penberthycroftite sample the phase transition to the DL phase occurs at a lower temperature of ∼80°C. The DL phase is stable to a temperature of ∼120°C. At higher temperatures, increased rotation of the columns is accompanied by a progressive amorphization of the sample. Bettertonite, penberthycroftite and the DL phase exhibit negative thermal expansion (NTE) along all three axes with large NTE coefficients, of the order of-100 x 10 -6 °C-1.

Keywords

penberthycroftitebettertonitehydrated aluminium arsenatesdehydration phase transitionsin situ synchrotron powder diffraction
Type
Research Article
Information
Mineralogical Magazine , Volume 80 , Issue 7 , December 2016 , pp. 1205 - 1217
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2016

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References

Betterton, J. (2000) Famous mineral localities: Penberthy Croft mine, St. Hilary, Cornwall, England. UK Journal of Mines and Minerals, 20, 7—37.Google Scholar
Buerger, M.J., Dollase, W.A. and Garacochea-Wittke, I. (1967) The structure and composition of the mineral pharmacosiderite. Zeitschrift fur Kristallographie, 125, 92–108.CrossRefGoogle Scholar
Evans, J.S.O. (1999) Negative thermal expansion materials. Journal of the Chemical Society, Dalton Transactions, 3317—3326.Google Scholar
Grey, I.E., Mumme, W.G., MacRae, C.M., Caradoc-Davies, T., Price, J.R., Rumsey, M.S. and Mills, S.J. (2013) Chiral edge-shared octahedral chains in liskeardite, [(Al,Fe)32(AsO4)18(OH)42(H2O)22]-52H2O, an open framework mineral with a pharmacoalumite-related structure. MineralogicalMagazine, 77, 3125—3135.Google Scholar
Grey, I.E., Kampf, A.R., Price, J.R. and MacRae, C.M. (2015a) Bettertonite, [Al6(AsO4)3(OH)9(H2O)5].11H2O, a new mineral from the Penberthy Croft mine, St. Hilary, Cornwall, UK, with a structure based on polyoxometalate clusters. Mineralogical Magazine, 79, 1849–1858.CrossRefGoogle Scholar
Grey, I.E., Brand, H.E.A., Rumsey, M.S. and Gozukara, Y. (2015b) Ultra-flexible framework breathing in response to dehydration in liskeardite, [(Al, Fe)16(AsO4)9(OH)21(H2O)n]-26H2O, a natural open-framework compound. Journal of Solid State Chemistry, 228, 146–152.CrossRefGoogle Scholar
Grey, I.E., Betterton, J., Kampf, A.R., Macrae, C.M., Shanks, F.L. and Price, J.R. (2016) Penberthycroftite, [Al6(AsSO4)3(OH)9(H2O)5]-8H2O, a second new hydrated aluminium arsenate mineral from the Penberthy Croft mine, St. Hilary, Cornwall, UK. Mineralogical Magazine, 80, 1149—1160.Google Scholar
Harries, J.R. and Ritchie, A.I.M. (1981) The use of temperature profiles to estimate the pyritic oxidation rate in a waste rock dump from an opencut mine. Water, Air and Soil Pollution, 15, 405–23.CrossRefGoogle Scholar
Lightfoot, P., Woodcock, D.A., Maple, M.J., Villaescusa, L.A. and Wright, P.A. (2001) The widespread occurrence of negative thermal expansion in zeolites. Journal of Materials Chemistry, 11, 212–216.CrossRefGoogle Scholar
Rodriguez-Carvajal, J. (1990) FULLPROF: a program for Rietveld refinement and pattern matching analysis, in: Proceedings of the Satellite Meeting on Powder Diffraction of the XV Congress of the IUCr, Toulouse, France, 1990.Google Scholar
Schmitt, B., Bronnimann, C., Eikenberry, E.F., Gozzo, F., Hormann, C., Horisberger, R. and Patterson, B. (2003) Mythen detector system. Nuclear Instruments and Methods in Physics Research, A501, 267–272.CrossRefGoogle Scholar
Wallwork, K.S., Kennedy, B.J. and Wang, D. (2007) The high resolution powder diffraction beamline for the Australian Synchrotron. AIP Conference Proceedings, 879, 879–882.CrossRefGoogle Scholar