Intrusive, or plutonic, igneous rocks form when magma cools slowly below the Earth’s surface. Most intrusive rocks have large, well-formed crystals. Examples include granite, gabbro, diorite and dunite. ntrusive rock forms within Earth‘s crust from the crystallization of magma. Many mountain ranges, such as the Sierra Nevada in California, are formed mostly from large granite (or related rock) intrusions; see Sierra Nevada batholith.
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Journal of Geology and Geoscience 