Andesite from typical inclusion in lavas of Double Point dacite. Color: dark gray (N 3). Texture: miarolitic intersertal. Pore space, miarolitic cavities: 20-30 percent. Plagioclase lathes, 45-55 percent, average An60 but range from An26 to An74; megaphenocrysts, 3 percent, show fritted texture. Oxyhornblende, 14 percent, is pleochroic in deep brown and olive brown, occurs in needles with a length-width ratio of 15:1; many hornblende crystals have hollow centers. Orthopyroxene, 6 percent, occurs in euhedral needles with a length-width ratio as much as 30:1. Clinopyroxene, 4 percent, is present as stubby subhedral crystals. Magnetite, 4 percent, anhedrons have a length-width ratio as much as 10:1. Clear brown glass, 14 percent, in groundmass bas N=1.498.
Geology of Little Sitkin Island, Alaska