Chemistry of feldspars in the Ilímaussaq augite syenite with additional data on some other minerals

Abstract

The feldspars af the augite sycnitc have been described by Ussing (1912, p. 188), Hamilton (1964) and Ferguson (1964, 1970, pp. 49-51). These allthors used optical and X-ray methods giving only crude clues to chemistry. However, Hamilton (1964, pp. 28-29) noted the scarce occurrence ef corroded oligoclase cores, and Ferguson (1970) nored that the Ab/Or ratio is higher in feldspar from the augite syenite than in feldspar from the agpaitic rocks. Belaw are reported the results af a microprobe reconnaissance study ef feldspars from the augitc syenite, together witil microprobe data on some other minerals. Thc two samples selected are the same as used in a previous investigation of the mafic minerals (Larsen, 1976).