Synonym Discussion of NORMAL. regular, normal, typical, natural mean being of the sort or kind that is expected as usual, ordinary, or average. regular stresses conformity to a rule, standard, or pattern.
Extrusive Igneous Rocks. VOLCANOES! Extrusive igneous rocks form when magma reaches the Earth's surface a volcano and cools quickly. Most extrusive (volcanic) rocks have small crystals. Examples include basalt, rhyolite, andesite, and obsidian. Mineral Photos courtesy of R.Weller/Cochise College.
Underground, they are formed when magma deep within the Earth becomes trapped in small pockets. As these pockets of magma cool slowly they become igneous rocks. Igneous rocks are also formed when volcanoes erupt. Igneous rocks are formed as the lava cools above ground.The upper 16 km of the Earthâs crust is composed of 95% igneous rock.Intrusive igneous rocks are formed from magma that cools and solidifies underground.oarse grained intrusive igneous rocks which form deep in the crust are termed as abyssal and those that form near the surface are called hypabyssal. Extrusive igneous rocks are formed at the crustâs surface as a result of the partial melting of rocks within the mantle and crust.