ˈär(ˌ)sōˌīt noun
( -s )
Etymology: German arsoit, from Arso, town on the island of Ischia, Italy + German -it -ite
: a dark gray porous rock consisting of trachyandesite containing phenocrysts of andesine, sanidine, diopside, and a little olivine in a trachytic groundmass of sanidine, a little oligoclase, much diopside, and magnetite