Felsite is fine grained but not glassy, and it may or may not have phenocrysts (large mineral grains). It is high in silica or felsic, typically consisting of the minerals quartz, plagioclase feldspar and alkali feldspar. Felsite is usually called the extrusive equivalent of granite.
A common felsitic rock is rhyolite, which typically has phenocrysts and signs of having flowed. Felsite should not be confused with tuff, a rock made up of compacted volcanic ash that can also be light colored.
For photos of related rocks, see the extrusive volcanic rocks gallery.
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Geologic Features and Processes
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Geology and Society
