How are igneous rocks formed? Igneous Rocks: Formation Through Cooling of Magma

Igneous Rocks: Formation Through Cooling of Magma

Igneous rocks are one of the three main rock types that are classified based on the way they are created. Igneous rocks are formed through the cooling and solidification of magma or lava. Magma is molten rock material found below the Earth’s surface and is formed when minerals, gases, and water molecules in the Earth’s mantle and core become unstable as a result of heat and pressure. The magma is then forced through cracks and fissures in the Earth’s surface, where it cools and solidifies to form igneous rocks. The rate at which magma cools affects the type of igneous rock that is formed. Magma that cools slowly beneath the Earth’s surface allows for large crystals to form, while magma that cools quickly at the surface forms smaller crystals. The size of the crystals affects the texture of the igneous rock and can range from fine-grained to coarse-grained. For example, basalt and granite are both igneous rocks; however, basalt, which cools quickly at the surface, has a fine-grained texture, while granite, which cools slowly below the surface, has a coarse-grained texture (Geology.com, n.d.; National Park Service, n.d.). In addition to texture, the composition of the magma also affects the type of igneous rock that is formed. Magma with a high silica content is more viscous and is likely to form intrusive rocks, while magma with a low silica content is less viscous and is likely to form extrusive rocks (National Park Service, n.d.). Cont…