Affiliation: | a Birkbeck/UCL Research School of Geological and Geophysical Sciences, Malet Street, London, WCIE 7HX, UK b Department of Geology, Royal Holloway, University of London, Egham Hill, Egham, 7W20 0EX, UK c Department of Mineralogy, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK |