Subsolidus Crystallization Behaviour in the System KAlSi3O8-NaAlSi3O8-H2O

Ian Parsons
Department of Geology and Mineralogy, Marischal College, Aberdeen AB9 1AS

Summary: When gels and glasses of alkali feldspar composition are crystallized hydrothermally below their solidus the crystals present when crystallization is incomplete do not have the same Na:K ratio as the starting material but bear a relation to the starting material analogous to that between crystals and liquids coexisting at the liquidus. This effect has been investigated in the temperature range 700–850 °C at water-vapour pressures between 5000 lb/in.2 and 30000 lb/in.2 Fractionation and normal zoning of crystals may, in principle, occur within fixed bulk compositions held under isothermal, isobaric conditions.

Mineralogical Magazine; June 1969 v. 37; no. 286; p. 173-180; DOI: 10.1180/minmag.1969.037.286.03
© 1969, The Mineralogical Society
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