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Astrophyllite from Kangerdlugssuaq, East Greenland

Published online by Cambridge University Press:  05 July 2018

Graham D. Layne ,
John C. Rucklidge  and
C. Kent Brooks
Graham D. Layne
Affiliation:
Department of Geology, University of Toronto, Toronto, Canada, M5S 1A1
John C. Rucklidge
Affiliation:
Department of Geology, University of Toronto, Toronto, Canada, M5S 1A1
C. Kent Brooks
Affiliation:
Institut for Petrolgi, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark
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Abstract

Astrophyllite has been found in alkalic pegmatite dykes on the two sides of Kangerdlugssuaq fjord. At the eastern locality, Kraemers Island, the dyke is silica oversaturated and the astrophyllite occurs in a broad tabular crystal habit. The dyke at the western locality, Bagnaesset, is silica undersaturated and the astrophyllite occurs in elongated prisms of acicular habit. Electron probe analyses of the crystals of the two habits have shown systematic chemical differences which not only relate to Mn and Ti compositional variations, but also reveal departures from ideal stoichiometry in varying degrees. Based on this latter feature a model involving polysomatism has been constructed which may explain the differences in crystal habit.

Type
Research Article
Information
Mineralogical Magazine , Volume 45 , Issue 337 , 1982 , pp. 149 - 156
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1982

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