| Text Description: |
High-silica dacite of Double Point dacite. Color: medium dark gray (N 4). Texture: hypocrystalline, porphyritic with blocky feldspar phenocrysts with maximum diameter of 5 mm. Eleven sections of the plagioclase, 25-30 percent, perpendicular to both albite twinning and basal cleavage give anorthite contents that appear to be distributed evenly from An23 to A55; complex zones and intergrowths common; groundmass microlites may group around An17 but cannot be determined accurately; two-fluid inclusions from 0.004-0.02 mm in diameter occupy negative crystals in certain zones of the feldspar. Stubby euhedral hypersthene, 5-10 percent, is pleochroic in light pink and light green. Accessories are clinopyroxene, 1 percent; magnetite, 2 percent; oxyhornblende, 1 percent; and tridymite, 1 percent. Fluidal groundmass glass has N=1.504(?). |
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