gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1967.036.278.05 A Second Occurrence of Dalyite and the Petrology of Some Ejected Syenite Blocks from São Miguel, Azores Cann J. R. Department of Mineralogy and Petrology, Downing Place, Cambridge1

Present address: British Museum (Natural History), London, S.W. 7.

 6 1967 36 278 227 232 6 10 1966 Copyright © 1967, The Mineralogical Society 1967 Summary

Dalyite, K2ZrSi6O15, occurs in the ejected syenite blocks of Serra de Agua de Pau (Lagoa do Fogo), São Miguel, Azores, in an assemblage sanidine-arfvedsonite-quartz-aegirine-fayalite-astrophyllite-dalyite-pyrrhite. Other blocks from the same locality contain biotite-zircon in place of astrophyllite-dalyite. A comparison made between the chemistry of one specimen of each type indicates that they may be related by paraeutectoid fractional crystallization.