San Marcos Gabbro
Field Collector: Esper Signius Larsen Jr.
Place Collected:Near Pala, San Luis Rey Quadrangle, Southern California
Object number: ROC21756
DescriptionGrey medium-grained (1-5 mm) plutonic rock. According to Larsen (1948) it consists of 67% plagioclase, 18% olivine, 10% hornblende, 2% hypersthene (orthopyroxene), 1.5% spinel, 1% Fe-ore, and 0.5% iddingsite (alteration of olivine).