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Granodiorite Porphyry of Santa Margarita Mountains
Field Collector: Esper Signius Larsen Jr.
Place Collected:Somewhere in the Santa Margarita Mountains, San Luis Rey Quadrangle, Southern Califronia
Object number: ROC21752
DescriptionLight grey porphyritic plutonic igneous rock. Mineral modes given by Larsen (1948) are 17% plagioclase phenocrysts, groundmass of 45% othoclase, 24% quartz, 8% plagioclase, 2% hornblende, 2% epidote, 1% biotite, and 1% opacite (unidentified black mineral grains). The porphyritic nature of this rock is not obvious in hand specimen.
In Collection(s)