| Text Description: |
Medium light-gray (N6) hypersthene andesite, conspicuously porphyritic and irregularly vesicular. Phenocrysts include plagioclase, augite, hypersthene, and hornblende. Plagioclase is labradorite with a median composition of An53, in crystals ranging in size from 0.1 to 2mm, commonly zoned, with the sequence of zones differing from one crystal to another. Salite, in dark-green crystals ranging in size from 0.1 to 0.5 mm, has nZ 1.712, suggesting a composition of Ca50Mg38Fe12. Hypersthene has nZ equal to 1.70, suggesting a composition of En72Fs28. Many of the hypersthene crystals have jackets of augite. The hornblende crystals are considerably resorbed, and are pleochroic from dark reddish-brown to yellow. The accessory minerals are magnetite or ilmenite, and psudodichroic apatite prisms. The groundmass consist of plagioclase crystals and augite needles in pale-brown glass whose index ranges from 1.50 to 1.495. |