Andesite, Sutter Buttes, California
Picture Gallery of Volcanic Rocks
By Andrew Alden, About.com Guide
Andesite (specimen from Sutter Buttes) is more siliceous and less fluid than basalt. Large light phenocrysts are potassium feldspar. Andesite can also be red.
Photo (c) 2007 Andrew Alden, licensed to About.com
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