Granodiorite
Field Collector: Esper Signius Larsen Jr.
Place Collected:Near Escondido, CA, San Luis Rey Quadrangle, California
Object number: ROC21684
DescriptionPlutonic,medium-grained (1-5 mm), igneous rock that is black and white on a fresh surface and black and grey on a weathered surface. Consists of 49% white feldspar (1-2 mm), 30% light-medium grey quartz (1-4 mm), 10% black biotite (1-2 mm), 10% black honblende (1-2 mm), and 1% brown pyroxene (2 mm). The pyroxene is rimmed by hornblende and biotite. The different feldspars are not distinctly different in handsample because they are small and the same color.