A Second Occurrence of Dalyite and the Petrology of Some Ejected Syenite Blocks from São Miguel, Azores

J. R. Cann
Department of Mineralogy and Petrology, Downing Place, Cambridge1
1Present address: British Museum (Natural History), London, S.W. 7.

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.

Mineralogical Magazine; June 1967 v. 36; no. 278; p. 227-232; DOI: 10.1180/minmag.1967.036.278.05
© 1967, The Mineralogical Society
Mineralogical Society (www.minersoc.org)