Low-silica dacite of Little Sitkin dacite. Color: medium gray (N 5). Texture: hypocrystalline, massive. Plagioclase, 20 to 25 percent, ranges in composition from An55 to An72; a few have fritted centers. Orthopyroxene, 2-3 percent, and clinopyroxene, 2-3 percent, both distinctly pleochroic in light pink and light green; a few orthopyroxene and clinopyroxene centers in differently oriented clinopyroxene crystals. One relict olivine grain, with a thick reaction rim of pyroxene and magnetite. No oxyhornblende xenocrysts although this mineral is plentiful in nearby thin laminae of rhyodacite. Groundmass brownish glass filled with magnetite dust and crystallites.
Geology of Little Sitkin Island, Alaska