gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1958.031.242.02 New Data for Dumortierite Claringbull G. F. B.Sc., Ph.D., A.Inst.P. Hey M. H. M.A., D.Sc. Department of Mineralogy, British Museum. 9 1958 31 242 901 907 Copyright © 1958, The Mineralogical Society 1958 Summary

New chemical, optical, and X-ray data have been obtained for dumortierite. The unit cell. space group Pemn, contains 4[(Al,Fe)7BSi3O18]. Brown gem quality material from Ceylon has α 1·6860, black, [001], β 1·722, deep redbrown, and γ, 1d7229, brown, with 2Vα 13° , γ > υ. X-ray powder data are given.