Aegirine and riebeckite of the alkali gneiss of Pikkukallio in the Honkamäki-Otanmäki region, Finland

K. Hytönen, T. Hautala
1985 Bulletin of the Geological Society of Finland  
TUULA, 1985: Aegirine and riebeckite of the alkali gneiss of Pikkukallio in the Honkamäki-Otanmäki region, Finland. Bull. Geol. Soc. Finland 57, Part 1-2, 169-180. Aegirine and riebeckite coexist in a Precambrian peralkaline gneiss. Chemical analyses of the gneiss and chemical and physical data on the aegirine and the riebeckite are presented. The compositions of the two minerals are compared with those of other sodic pyroxenes and alkali amphiboles from Finland. The authors know of only two
more » ... know of only two other occurrences in Finland where sodic pyroxene and alkali amphibole coexist. The riebeckite of the present study and the ferro-ferribarroisite of the adjoining Otanmäki are richer in iron and poorer in magnesium and calcium than the other known alkali amphiboles and sodic-calcic amphiboles from Finland. Zircon age of 2019 Ma has been obtained for a variety of the alkali gneiss of the region.
doi:10.17741/bgsf/57.1-2.014 fatcat:yxtqu4rcazgenbi63m7yfgi7jy