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

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dc.contributor.authorGrey, IEen_AU
dc.contributor.authorBrand, HEAen_AU
dc.contributor.authorBetterton, Jen_AU
dc.date.accessioned2021-12-07T03:52:00Zen_AU
dc.date.available2021-12-07T03:52:00Zen_AU
dc.date.issued2016-12en_AU
dc.date.statistics2021-11-08en_AU
dc.description.abstractBettertonite, [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. © 2016 The Mineralogical Society of Great Britain and Irelanden_AU
dc.identifier.citationGrey, I. E., Brand, H. E. A. & Betterton, J. (2016). Dehydration phase transitions in new aluminium arsenate minerals from the Penberthy Croft mine, Cornwall, UK. Mineralogical Magazine, 80(7), 1205-1217. doi:10.1180/minmag.2016.080.126en_AU
dc.identifier.issn0026-461Xen_AU
dc.identifier.issue7en_AU
dc.identifier.journaltitleMineralogical Magazineen_AU
dc.identifier.pagination1205-1217en_AU
dc.identifier.urihttps://doi.org/10.1180/minmag.2016.080.126en_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/12369en_AU
dc.identifier.volume80en_AU
dc.language.isoenen_AU
dc.publisherCambridge University Pressen_AU
dc.subjectPhase transformationsen_AU
dc.subjectDehydrationen_AU
dc.subjectSynchrotronsen_AU
dc.subjectX-ray diffractionen_AU
dc.subjectMineralsen_AU
dc.subjectAluminiumen_AU
dc.subjectUnited Kingdomen_AU
dc.subjectMinesen_AU
dc.titleDehydration phase transitions in new aluminium arsenate minerals from the Penberthy Croft mine, Cornwall, UKen_AU
dc.typeJournal Articleen_AU
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