gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1972.038.299.04 Alkali Feldspars from Part of the Galway Granite, Ireland Wilson J. R. Geologisk Institut, Aarhus Universitet, Ole Worms Alle, 8000 Århus C, Denmark Coats J. S. Institute of Geological Sciences, 64-78 Grays Inn Road, London W.C. I, Great Britain 9 1972 38 299 801 810 19 6 1971 Copyright © 1972, The Mineralogical Society 1972 Summary

The structural states of alkali feldspars from the eastern end of the Galway Granite show transitions from orthoclase to microcline as a result of late deformation. Analyses of twenty samples for SiO2, Al2O3, TiO2, Fe2O3, CaO, Na2O, K2O, S, Cu, Zn, Ga, Rb, Sr, Ba, and Pb agree with previously determined orders of entry of elements into the ‘alkali site’. A relationship between this order of entry and the melting points of feldspar end-members is discussed.