| Plutonic rock in North America | examples and Chemical classification also extends to differentiating rocks that are chemically similar according to the TAS diagram, for instance;• |
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| While cooling, the magma evolves in composition because different minerals crystallize from the melt | examples , and• 1: crystallizes; 2: olivine and crystallize; 3: pyroxene and crystallize; 4: plagioclase crystallizes |
This is not an exact method, because the classification of igneous rocks also depends on other components than silica, yet in most cases it is a good first guess.
21| examples and Chemical classification also extends to differentiating rocks that are chemically similar according to the TAS diagram, for instance;• Basic classification scheme for igneous rocks on their | Le Maitre editor 2002 Igneous Rocks: A Classification and Glossary of Terms, Recommendations of the International Union of Geological Sciences, Subcommission of the Systematics of Igneous Rocks |
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| At the bottom of the magma reservoir, a forms | Chemical: total alkali-silica content for classification used when modal or mineralogic data is unavailable:• Le Maitre editor 2002 Igneous Rocks: A Classification and Glossary of Terms, Recommendations of the International Union of Geological Sciences, Subcommission of the Systematics of Igneous Rocks |
If the approximate volume fractions of minerals in the rock are known, the rock name and silica content can be read off the diagram.
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