Slightly altered feldspathic basalt porphyry. It is greenish gray to grayish green and contains phenocrysts 1 to 2 millimeters long. Phenocrysts compose 15 percent of the rock : 12 percent sodic labradorite, which forms embayed crystals, euhedral laths, and irregular grains and which contains normal and oscillatory zones and zones of dusty inclusions ; 3 percent angite or diopside, which form euhedral to anhedral crystals and crystal clusters and which alter to chlorite and uralite(?) pseudomorphs ; and a trace of olivine (?) , which appears as chlorite and uralite(?) pseudornorphs. The groundmass has a felty to granular texture and consists of plagioclase, altered pyroxene(?), and a black opaque mineral. Alteration is moderate ; chlorite and uralite (?) replace pyroxene
and olivine (?) .
Geology of Unalaska Island and adjacent insular shelf, Aleutian Islands, Alaska