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 TiO
2 (1.65-5.06 wt%) and Al
2O
3 (10.44-14.98 wt%). The fassaitic augite core has lower mg value (100 Mg/(Mg+Fe
2+) =52.4-67.2) and higher Na
2O 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.
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