Andalusite, Kyanite, and Sillimanite from the Mount Moosilauke Region, New Hampshire
Andalusite, kyanite, and sillimanite occur in regionally metamorphosed rocks of the Mount Moosilauke region, New Hampshire. Andalusite and sillimanite are found together frequently in the same thin sections. Kyanite appears once in the same thin section with sillimanite but never with andalusite. Andalusite and sillimanite mica schists were subjected to multiple episodes of recrystallization that resulted in the reaction sequence andalusite → sillimanite → andalusite. Kyanite crystallized in an adjacent area during the same time period. Kyanite from quartzite containing hematite is enriched in Fe2O3 but andalusite. and sillimanite from rutile and ilmenite—or graphite-bearing mica schists—are relatively impoverished in Fe2O3. The Al2SiO5 minerals crystallized during post-Lower Devonian, pre-Triassic regional metamorphism under conditions approaching chemical equilibrium.