21.3.1 Slightly porphyritic, flow-banded alkali rhyolite. Nuns Canyon, Kenwood, California. Goethite (?) coats orange-weathered, vesicular, flow-band surfaces on which minor, tiny aegirine crystals are present as black grains. A few sanidine crystals form small phenocrysts, one of which, in the upper center of the sample, reflects light from a cleavage surface.