gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1971.038.295.05 The Stability and Natural Occurrence of Margarite Velde Bruce Laboratoire de Pétrographie, Faculté des Sciences de Paris, 9 quai Saint Bernard, Paris 5 9 1971 38 295 317 323 1 5 1970 Copyright © 1971, The Mineralogical Society 1971 Summary

The upper stability of margarite has been determined to be 450 °C at 1 kb and 530 °C at 2 kb total pressure (PH2O = Ptotal). Other experiments delimit in a general way the lower stability of this mineral and its paragenesis in more SiO2 rich compositions. The presence of the 060 reflection at 1·475 Å can be used to distinguish between margarite and paragonite or muscovite.