Igneous Rock

Igneous swings originate from deep within the universes crust. Igneous rocks (from the Greek word for fire) are organise when magma crystallizes and solidifies. An increase in temperature, a change in the composition, or decrease in the compact can cause melting of these rocks in the mantle which form pyrogenic rocks. The melt begins deep below the surface of the Earth close to progressive plate boundaries. As the temperate increases the rocks rise toward the surface.Igneous rocks are divided into 2 categories, scrutinizing or extrusive, depending on where the magma solidifies (USGS, 2004). peeping or plutonic pyrogenic rocks form when magma cools and solidifies beneath the surface of the Earth. These types of rocks cool very slowly and pass on mineral grains that can usually be seen with the naked eye. Intrusive rocks pretend a loose grained texture. One example of an intrusive pyrogenetic rock would be granite. Extrusive, or volcanic, igneous rocks are formed when mag ma exits and cools outside of the Earths surface.These types of rocks are formed when lava flows from volcanoes. They solidify above the surface and claim much shorter cooling times. Because lava cools and crystallizes quickly, it is a fine grain. The grains in extrusive rocks are quite small, so to classify them they have to be placed under a microscope to examine the thin sections to determine the mineral constituents. Given that igneous rocks form from a liquid state, their mineral grains are packed unitedly very tightly (Geo. a, n. d. ). One distinguishing characteristic between the two categories of rocks is that intrusive rocks are formed below the surface and extrusive rocks are formed above the surface. Another distinguishing characteristic is that intrusive rocks have a coarse grained texture and extrusive rocks have a fine grain texture. Intrusive rocks cool and solidify very slowly whereas extrusive rocks have a much shorter cooling time which means they solidify faste r.Reference Geology in the bailiwick Parks (January 13, 2004) Rocks. Retrieved March 24, 2010 from http//geomaps.wr.usgs.gov/parks/rxmin/rock.html Igneous Rocks (n.d.) What are Rocks. Retrieved March 24, 2010 from http//www.geo.ua.edu/intro03/ignis.html