What is Igneous Rock?
Igneous rocks are formed when molten rock (magma) cools and solidifies, 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 either the Earth’s mantle or pre-existing rocks made molten by extreme temperature and pressure changes. Over 700 types of igneous rocks have been described, most of them formed beneath the surface of the Earth’s crust. The word “igneous” is derived from the Latin ignis, meaning “fire”. |Magma origination| The Earth’s crust is about 35 kilometers (22 miles) thick under the continents, but averages only some 7 kilometers (4.3 miles) beneath the oceans. It is made up of rocks which have a relatively low density, and beneath the crust there is the denser rock of the mantle, which extends to a depth of nearly 3,000 kilometers (1,860 miles). Most of the magma which forms igneous rocks is generated within the upper parts of the mantle at temperatures estim
Igneous rock is one of three basic kinds of rock, along with sedimentary and metamorphic rock. The word igneous comes from the Latin word, ignis, which means fire. Igneous rocks are rocks which were once molten inside the earth. There are over 700 different kinds of igneous rock. Two well known examples are granite and basalt. All of the many different kinds of igneous rock can be subdivided into one of two categories: intrusive rock and extrusive rock. Intrusive rock hardens and forms below the earths surface. Extrusive rock forms on the Earths surface. Intrusive rock is also called plutonic rock, named after Pluto, the Roman god of the Underworld (because Plutonic rock forms beneath the earths surface). Extrusive rock is also called volcanic rock, named after Vulcan, the Roman god of fire, because volcanic rock is spewed onto the earths surface by volcanic activity which is also named after Vulcan. There it cools becoming extrusive rock. Many scientists believe that by using radiomet
Igneous rock forms when molten minerals cool from a liquid into a solid. Above ground, the molten rock takes the form of lava spewing from volcanic fissures while below ground, magma cools in small caves of air. These processes form volcanic or plutonic rock, respectively. Igneous comes from the root word “ignis,” which means, “of fire,” which differentiates this form of rock from sedimentary or metamorphic rock. The asthenosphere, part of the earth’s mantle, is made of liquefied rock known as magma that churns at temperatures between 1100-2400° F (590-1300° C). Sometimes the magma reaches hollow parts in cooler rocks through the movement of tectonic plates. It slowly cools, hardening and crystallizing into intrusive rock also called plutonic igneous. In more dramatic geologic shifts, volcanoes eject lava to the open air where it cools much more quickly into extrusive, volcanic igneous. Different types of rocks can be identified by their composition, the kind of minerals they join, and
