Metamorphic rock

"Metamorphic" redirects here. For other uses, see Metamorphic (disambiguation).

Quartzite, a type of metamorphic rock
Metamorphic rock, deformed during the Variscan orogeny, at Vall de Cardós, Lérida, Spain

Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than 150 to 200 °C (300 to 400 °F) and, often, elevated pressure of 100 megapascals (1,000 bar) or more, causing profound physical or chemical changes. During this process, the rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition.[1] The protolith may be an igneous, sedimentary, or existing metamorphic rock.

Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface.[2] They are classified by their protolith, their chemical and mineral makeup, and their texture. They may be formed simply by being deeply buried beneath the Earth's surface, where they are subject to high temperatures and the great pressure of the rock layers above. They can also form from tectonic processes such as continental collisions, which cause horizontal pressure, friction, and distortion. Metamorphic rock can be formed locally when rock is heated by the intrusion of hot molten rock called magma from the Earth's interior. The study of metamorphic rocks (now exposed at the Earth's surface following erosion and uplift) provides information about the temperatures and pressures that occur at great depths within the Earth's crust.

Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartzite. Slate[3] and quartzite[4] tiles are used in building construction. Marble is also prized for building construction[5] and as a medium for sculpture.[6] On the other hand, schist bedrock can pose a challenge for civil engineering because of its pronounced planes of weakness.[7]

  1. ^ Yardley, B. W. D. (1989). An introduction to metamorphic petrology. Harlow, Essex, England: Longman Scientific & Technical. p. 5. ISBN 0582300967.
  2. ^ Wilkinson, Bruce H.; McElroy, Brandon J.; Kesler, Stephen E.; Peters, Shanan E.; Rothman, Edward D. (2008). "Global geologic maps are tectonic speedometers – Rates of rock cycling from area-age frequencies". Geological Society of America Bulletin. 121 (5–6): 760–79. doi:10.1130/B26457.1.
  3. ^ Schunck, Eberhard; Oster, Hans Jochen (2003). Roof Construction Manual : Pitched Roofs (2003 ed.). München: DE GRUYTER. ISBN 9783034615631.
  4. ^ Powell, Darryl. "Quartzite". Mineral Information Institute. Archived from the original on 2009-03-02. Retrieved 2009-09-09.
  5. ^ "Marble" (PDF). Glossary of Terms. Marble Institute of America. p. 23-15. Retrieved 28 February 2021.
  6. ^ PROCEEDINGS 4th International Congress on "Science and Technology for the Safeguard of Cultural Heritage in the Mediterranean Basin" VOL. I. Angelo Ferrari. p. 371. ISBN 9788896680315. white marble prized for use to make sculptures.
  7. ^ Zhang, Xiao-Ping; Wong, Louis Ngai Yuen; Wang, Si-Jing; Han, Geng-You (August 2011). "Engineering properties of quartz mica schist". Engineering Geology. 121 (3–4): 135–149. doi:10.1016/j.enggeo.2011.04.020.