Sedimentary Analcime Rocks and Sodium-rich Gneisses

D. S. Coombs
Geology Department, University of Otago

Summary: As indicated by Tilley (1925), albite-rich schists and gneisses can inherit their abnormal chemical characteristics from sediments that are proving to be by no means rare. They may be rich in detrital sodic plagioclase or they may contain authigenie anaicime. Some sedimentary analcime rocks (‘analcimolites’) carry normative nepheline and so offer potential parent rocks for nepheline-bearing gneisses provided that, in these gneisses, SiO2 ⩾ (4Na2O+6K2O) in molecular proportions. The chemistry and occurrence of soda-rich sediments are reviewed. Some New Zealand occurrences are newly described and hitherto unpublished analyses are presented for porphyroblastic abite schist and felsitic volcanic arenite from Otago, and for analcime-rich sediments from four localities.

Mineralogical Magazine; 1965 v. 34; no. 268; p. 144-158; DOI: 10.1180/minmag.1965.034.268.12
© 1965, The Mineralogical Society
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