The Origin of Garnets in the Borrowdale Volcanic Series and Associated Rocks, English Lake District

Abstract

Almandine-rich garnets occur as euhedral crystals in extrusive and intrusive rocks which range in composition from 59 per cent, to 70 per cent. SiO2. Eight complete garnet analyses (major and trace elements) indicate a small variation in composition which, together with corresponding variation of physical properties, appear to correlate with the mineralogical composition of the containing rock. Field, microscopic and chemical evidence suggests, on balance, that the garnets are pyrogenetic. Magmatic conditions suitable for the crystallisation of almandine-rich garnet are discussed.