igneous rocks
metamorphic rocks
sedimentary rocks
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Description
A fine grained (aphanitic) igneous rock, white, light gray, pink, to dark in color. Phenocrysts (large visible crystals) are often present
Since color is such a poor indicator of rock identification in most cases, darker rhyolites can be confused with lighter andesites. Felsite is the general term for an unidentifiable, fine grained, generally middle colored rock.
Typical Minerals
Minerals too small to identify (except phenocrysts). Composition will be from bottom of Bowen's Reaction series (i.e. felsic).
Tectonic Association
rhyolite, as with all felsic rocks, is found on continents, ejected from volcanoes.
Another Sample
Description
A fine grained (aphanitic) igneous rock, white, light gray, pink, to dark in color. Phenocrysts (large visible crystals) are often present, such as in this specimen (although the larger chunks may be pyroclastics, volcanic ejecta, rather than true phenocyrsts.)
Since color is such a poor indicator of rock identification in most cases, darker rhyolites can be confused with lighter andesites. Felsite is the general term for an unidentifiable, fine grained, generally middle colored rock.
Description
A fine grained (aphanitic) igneous rock, white, light gray, pink, to dark in color. orthoclase phenocrysts are present in this specimen.
Color is such a poor indicator of rock identification in most cases, that it can only be a first approximation. Here, however, the orthoclase phenocrysts put it in the felsic range, although without knowing the quartz content we do not know if a phaneritic variety would be syenite or alkali granite.
Detail
Description
In this detail orthoclase phenocrysts are clearly seen, indicating this rock underwent a two stage cooling. |