Igneouse Rock, info and formation
Posted: Tuesday, April 05, 2005
by Joey Lewitin
Stone Coasters
Igneous is a word that refers to formation from flame. An igneous rock is a rock that has formed from the cooling of liquid magma. If this cooling occurs above the surface of the earth it is called an extrusive igneous rock. It the cooling occurs slowly beneath the surface of earth then it is an intrusive rock, and will most probably have large grains that can be seen with the eye.. It is formed from different elements which combine under the intense heat.
Igneous rocks are classified by the size of the grains in their structure. Some of these rocks are equigranular, and have uniform grain sizes. Others have Phenocrysts, which are irregularly large grains found in the surface of some igneous rocks. These irregularities demonstrate the double process which some igneous rocks undergo, where they are at first extremely hot, and then slowly cool down. It is during the slow cooling down stage that Phenocrysts can form in the surface of these rocks.
Igneous rocks can range from glassy in color, to light white, to dark black, depending on their formation and their components. The Phenocrysts can look completely different from their surrounding materials. Alkali feldspars cause it to be light, and iron or calcic deposits can cause a darker color. Some common forms of igneous rock are Syenite, Granite, pumice, pitchstone, Trachite, and basalt. Exceptions to classification rules for igneous rocks include obsidian and Scoria.
These rocks provide a great example of the ways that rocks can change over time into other rocks. Sedimentary or metamorphic rocks can, under heat, change into a completely different igneous rocks, which can then change into other forms.
This article was good
this artical is good, and it may better if give some brife information about the chemical classification ot the igneouse rocks.