Sample of a dense flow of phyric hyalobasanite. Olivine, augite, and plagioclase occur as phenocrysts. Augite is commonly twinned, ??c=43 degrees, (+) 2V=50-55 degrees, r>v distinct. The plagioclase crystals are also twinned, extinction angles correspond to An60. In the groundmass the plagioclase ranges from An60-An35.
Geology and petrology of the Pribilof Islands, Alaska