Igneous Rock

one of the three main rock types that is formed by the forcing up of hot, molten rock (magma), from great depths, or lava flows on the surface associated with volcanoes.

Taken from Dictionary of Science

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Igneous rock (from the Latin ignis meaning born of fire) is one of the three main rock types (the others being sedimentary and metamorphic rock). Igneous rock is formed by magma (molten rock) cooling and becoming solid. Igneous rock may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be derived from partial melts of pre-existing rocks in either a planet's mantle or crust. Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Over 700 types of igneous rocks have been described, most of them having formed beneath the surface of Earth's crust. These have diverse properties, depending on their composition and how they were formed.

Taken from Wikipedia