Mineral Department, British Museum of Natural History.
with chemical analysis by M. H. Hey, B.A., B.Sc. 1A preliminary account was given in an appendix to Mr. Thomas's paper, ‘A camel journey across the Rub al Khali’, in the Geogr. Journ. London, 1931, vol. 78, pp. 236. There the specific gravity is given incorrectly.