Astrophyllite from Kangerdlugssuaq, East Greenland

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

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.

Mineralogical Magazine; 1982 v. 45; no. 337; p. 149-156; DOI: 10.1180/minmag.1982.045.337.17
© 1982, The Mineralogical Society
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