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Olivine-bearing andesite porphyry from a flow in the Eider Point basalt 1/2 mile southeast of Sugarloaf Cone. It is medium gray and contains plagioclase, olivine, and pyroxene phenocrysts 1-3 millimeters long. Phenocrysts compose 30 percent of the rock: 15 percent calcic andesine to sodic labradorite, which forms embayed crystals, euhedral laths, and fragments, and which has normal and oscillatory zones, zones of dusty inclusions, and apatite inclusions; 10 percent euhedral to anhedral augite(?), of which one crystal has a reaction rim of granular olivine, one crystal has an inner rim of granular olivine and an outer rim of clinopyroxene, and one crystal has a clinopyroxene rim; 3 percent subhedral hypersthene, which has augite(?) reaction rims, and one crystal of which has an olivine(?) and myrmekitic magnetite(?) rim; and 2 percent anhedral olivine with clinopyroxene reaction rims. The groundmass has a felty to granular texture and consists of abundant subhedral labradorite, much clinopyroxene and granular olivine(?), and traces of a granular black opaque mineral and cristobalite. |
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