Igneous rock is formed through the cooling and solidifying of lava. There are over 700 types of igneous rock. The upper ten miles of the earth’s crust is composed of 95% igneous rock. Some types of igneous rock are also known as volcanic rock.
Igneous rock is formed after the cooling and solidification of molten magma. Those formed inside the ground are called intrusive igneous roks while those formed on the surface of the earth’s crust are called extrusive igneous rocks.
Intrusive, or plutonic, igneous rocks are characterized by large mineral grains, due to the fact that the magma they originally were has cooled very slowly into rock form. A few types of plutonic rocks are granite, gabbro, pegmatite and granodiorite.
Igneous rocks of the extrusive, or volcanic, type are on the contrast cooled and formed into a solid quickly, as a result of the extreme difference in temperature between the internal volcano and the outside air. A smooth, shiny and sometimes bubble-textured appearance is common on these rocks. Basalt, pumice, andesite and dacite are some volcanic igneous rocks.
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