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How are igneous rocks classified?

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Igneous rocks are called intrusive when they cool and solidify beneath the surface. Intrusive rocks form plutons and so are also called plutonic. A pluton is an igneous intrusive rock body that has cooled in the crust. When magma cools within the Earth, the cooling proceeds slowly. read more

An igneous rock with larger, clearly discernible crystals embedded in a finer-grained matrix is termed porphyry. Porphyritic texture develops when some of the crystals grow to considerable size before the main mass of the magma crystallizes as finer-grained, uniform material. Igneous rocks are classified on the basis of texture and composition. read more

Igneous rock can additionally be classified by general chemistry composition as felsic, intermediate, mafic, and ultramafic. Felsic rocks are higher in silica and aluminum. Mafic rocks are higher in magnesium and iron. read more

Igneous rocks are classified on the basis of their composition and their texture. Magma, and the igneous rock it becomes, has a range of chemical compositions. For example, basalt is a mafic lava flow rock which originates from melting of the upper mantle. The way that magma turns into a solid rock gives it a distinctive igneous texture. read more

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