Article
Article
Igneous rock
Article By:
Raymond, Loren A. Department of Geology, Appalachian State University, Boone, North Carolina.
Last reviewed:November 2019
DOI:https://doi.org/10.1036/1097-8542.336700
Rock that has formed from melted rock, usually by cooling. The melted rock is called magma when it is below the surface, and lava when it flows out onto the surface. When the magma or lava cools or moves into areas of lower pressure, crystals or glass or both form. Thus, igneous rocks are composed of crystals, glass, or combinations of these materials. Magmas sometimes erupt explosively, creating ash that is composed of broken crystals, glass, and rock materials called pyroclastic material. Rocks formed at or very near the surface, including pyroclastic rocks, are called volcanic rocks, whereas those formed from magma at depth are called plutonic rocks. In the past, some rocks that formed below the surface but near it were called hypabyssal rocks. See also: Lava; Magma
The content above is only an excerpt.
About AccessScience
AccessScience provides the most accurate and trustworthy scientific information available.
Recognized as an award-winning gateway to scientific knowledge, AccessScience is an amazing online resource that contains high-quality reference material written specifically for students. Contributors include more than 10,000 highly qualified scientists and 46 Nobel Prize winners.
MORE THAN 8700 articles covering all major scientific disciplines and encompassing the McGraw-Hill Encyclopedia of Science & Technology and McGraw-Hill Yearbook of Science & Technology
115,000-PLUS definitions from the McGraw-Hill Dictionary of Scientific and Technical Terms
3000 biographies of notable scientific figures
MORE THAN 19,000 downloadable images and animations illustrating key topics
ENGAGING VIDEOS highlighting the life and work of award-winning scientists
SUGGESTIONS FOR FURTHER STUDY and additional readings to guide students to deeper understanding and research
LINKS TO CITABLE LITERATURE help students expand their knowledge using primary sources of information
