Fassaitic augite from Kajishi-yama basanite in Tsuyama Basin, Okayama Prefecture.

Fassaitic augite was found in the Kajishi-yama basanite from Tsuyama Basin, Okayama Prefecture, Southwest Japan. The fassaitic augite occures as follows; (1) An anhedral complex, zoned core, separated from the rim by a optically sharp boundary, (2) An outer most rim of clinopyroxene phenocryst. Both types of fassaitic augite are rich in TiO2 (1.65-5.06 wt%) and Al2O3 (10.44-14.98 wt%). The fassaitic augite core has lower mg value (100 Mg/(Mg+Fe2+) =52.4-67.2) and higher Na2O contents (1.54-2.09 wt%) than those of clinopyroxene phenocryst rim. The fassaitic augite core is considered to have crystallized from an evolved, strongly alkaline basaltic magma in a deep-seated magma chamber, and subsequently the magma might be mixed with the Kajishi-yama basanite magma from which the fassaitic augite rim was crystallized.