Olivine basalt porphyry from an Eider Point basalt flow three fourths mile southwest of Wide Bay Cone. It is medium gray and vuggy, and contains pyroxene and olivine phenocrysts 1-4 millimeters long. Phenocrysts compose 20 percent of the rock: 10 percent sodic bytownite, which forms euhedral laths, stubby crystals, and fragments, and which has normal zones, rare oscillatory zones, zones of dusty inclusions, and apatite inclusions; 5 percent augite(?), which forms euhedral to anhdral grains and embayed crystals, and which is faintly zoned; and 5 percent olivine, which forms subhedral to anhedral crystals and embayed crystals. The groundmass has an intergranular texture and consists of abundant stubby subhedral calcic andesine, much granular clinopyroxene and a black opaque mineral, and traces of olivine and tridymite.
Geology of Unalaska Island and adjacent insular shelf, Aleutian Islands, Alaska