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San Marcos Gabbro
Field Collector: Esper Signius Larsen Jr.
Place Collected:San Luis Rey Quadrangle, Southern California
Object number: ROC21760
DescriptionPlutonic medium-grained (1-5 mm) igneous rock. Dark salt and pepper on a fresh surface and dark grey on a weathered surface. Roughly consists of equigranular light grey plagioclase 60% (1-2 mm), black to brown amphibole or pyroxene 40%. According to Larsen (1948) mineral modes are 65% plagioclase, 28% hypersthene (orthopyroxene), 4% augite (clinopyroxene), 2% Fe-ore, 1% hornblende, and trace amounts of quartz, K-feldspar, and biotite.
In Collection(s)