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Dacite flows of Snider Peak - Massive dark gray weathering hornblende-rich flows that radiate from general area of Snider Peak dome. Flows are as much as a 100 m thick but appear to consist of complex multiple-flow cooling units suggesting possibility of more than one source, perhaps in part including second-cycle cone-building flows. They locally contain abundant concentrations of xenoliths and exhibit conspicuous columnar jointing. Rocks are light gray to pinkish medium gray with abundant medium (2-5 mm) phenocrysts of plagioclase and brown hornblende, minor to common hypersthene, and rare biotite, resorbed augite, and olivine generally in a feldspar-rich pilotaxitic to trachytic groundmass. Glassy phases have hyalopilitic and locally spherulitic groundmass textures. Chemistry: samples 23 (74-AMm-76B), 26 (74-ARh-310) |