Hornblende–cummingtonite and hornblende–actinolite intergrowths from the Koyama calc-alkaline intrusion, Susa, Southwest Japan Available to Purchase

Intergrowth and zoning of interstitial amphiboles in a quartz diorite of the Koyama calc-alkaline intrusion, Susa, southwest Japan indicate that hornblende in this rock initially crystallized in coexistence with cummingtonite, then changed in composition toward actinolite and was ultimately intergrown with hornblende of ferro-hornblende–ferro-actinolitic hornblende composition. The solidus of the interstitial residuum is considered to have crossed the hornblende–cummingtonite and the hornblende–actinolite solvi successively under conditions of high water pressure during the later stages of solidification of the quartz diorite. This suggests a petrogenetic significance of these solvi in controlling crystallization trends for intercumulus amphiboles in hydrous plutonic rocks.