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On the basis of the locale of origin the igneous rocks can be classified into intrusive and extrusive varieties. The intrusives crystallise beneath the surface and have a coarse texture. In contrast, the extrusive rocks crystallise on the surface, and have a finer texture.
Many of the intrusive rocks have their extrusive equivalents. Rhyolite and basalt are the the extrusive equivalents, respectively of granite and gabbro. Large masses of intrusive rock below the surface of the earth are called batholiths. Some cooled magma rises vertically to form projections called dikes. Some dikes have been uncovered by erosion and extend above the earth's surface. Diorite and andesite are intermediate between acidic and basic group.
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