Advanced Search
Indian Mountain Granodiorite
Field Collector: Esper Signius Larsen Jr.
Place Collected:Near Lancaster Mountain, near Pala CA, San Luis Rey Quadrangle, CA
Object number: ROC21678
DescriptionThis appears to be a gneiss because it has distinct light and dark layers, but the collector has identified it as a granodiorite. It is a foliated red-brown, rusty crumbling rock consisting of 30% layers of black fine-grained biotite (≤ 1 mm thick) in between a mixture of 30% light-grey quartz, 20% white plagioclase, and 20% light-tan K-feldspar (≤ 1 mm). All of the minerals are stained a rust color, there is no fresh surface. Larsen (1949) notes that "on Indian Mountain, the banding of the granodiorite is marked near the contact, and the rock might be called a gneiss."
In Collection(s)