Note on volcanic rocks, with special reference to plagioclase feldspars from Mt. Bog Ana, Bougainville Island, Solomon Islands

Abstract

Little is known of the petrology of the Quaternary‐Recent volcanoes on Bougainville Island. The purpose of this article is to record the nature of ejectamenta and lavas in the Mt. Bogana ‐ Torokina River area. Suggestions have been made herein concerning the origin of a mixed assemblage of non‐zoned, variously zoned, and twinned andesine phenocrysts contained in the lavas.The described rocks consist of ejected pebbles and andesitic scoria that form the greater part of the recent, symmetrical volcanic cone of Mt. Bogana (see Fig. 1), and slightly older andesitic flows that occur to the southwest in the valley of the Torokina River.