| Text Description: |
At least 20’ thick, plagioclase-phyric, locally glassy flow overlying lahar/pyroclastic flow that erodes into spires at Gutbuster. Fine grained, vesicular, holocrystalline, intersertal, porphyritic with a matrix of devitrified brown glass, plagioclase, clinopyroxene?, microlites and opaque. Plagioclase phenocrysts (An42 - An59) are up to 7.0 mm and commonly are oscillatory zoned, and occasionally have rounded, resorbed rims, or resorption embayments. Clinopyroxene phenocrysts are up to 1.4 mm. Orthopyroxene phenocrysts are up to 1.65 mm. Opaque phenocrysts are up to 0.65 mm. 70.0% matrix, 13.8% plagioclase, 1.8% clinopyroxene, 3.6% orthopyroxene, 1.7% opaque, 9.1% vesicles. Trachydacite. |