The Geology and Petrography of Crater Lake National Park, 1902
Augite is abundant, but is invariably much less so than plagioclase. It appears in thin section in pale-greenish or yellowish-green colors, and nearly always in small angular grains filling the spaces between the feldspar laths. Occasional exceptions to this rule may be mentioned (153) where the augite assumes in part roughly prismatic form, resembling that of the hypersthenes. It is invariably younger than the plagioclase and also younger than the hypersthene. In a few cases (156-157) contiguous or adjacent grains have simultaneous extinction, and develop into an ophitic structure through partially inclosed plagioclase laths. Augite is usually much more abundant than hypersthene, although it may become less so (152). As a general thing the augite is perfectly fresh, but brownish to deep-red iron oxide stains are common.