Albitized dacite porphyry from one-half mile west of Buttress Point and 10 1/2 miles southwest of Kuliliak Bay. It is brownish gray and has chalky plagioclase and ferromagnesian phenocrysts 1 to 2 millimeters long. Phenocrysts compose 1 percent of the rock, consisting of euhedral to subhedral laths and stubby crystals of albite with apatite inclusions and a trace of subhedral magnetite. The groundmass has an in distinct intersertal texture, consisting of abundant subhedral laths of albite and much interstitial altered glass, as well as traces of anhedral clinopyroxene, a granular black opaque mineral, 2nd interstitial quartz that may be primary and that has apatite inclusions. Alteration is intense; albite and kaolin are pervasive and abundant; quartz is common and interstitial; and there are traces of chlorite and uralite (?) altering clinopyroxene.
Geology of Unalaska Island and adjacent insular shelf, Aleutian Islands, Alaska