Sample of a glassy olivine basalt, Pribilof type, that is a vesicular gray flow or sill of a glassy basaltoid rock. The only crystalline silicates are olivine in small grains measuring about 0.05 mm across, and plagioclase in laths about 0.07 x 0.01 mm. They line in a glassy, inhomogeneous matrix containing ore and apatite in distinct crystals, and various unidentified products of incipient crystallization. The Pribilof type basaltoid lava flows have olivine, plagioclase, and glass as the only essential phases.
Geology and petrology of the Pribilof Islands, Alaska