Skip to main content
Select Source:

Metamorphic Rock

Metamorphic rock

Metamorphic rock is rock that has changed from one type of rock into another. The word metamorphic (from Greek) means "of changing form." Metamorphic rock is produced from either igneous rock (rock formed from the cooling and hardening of magma ) or sedimentary rock (rock formed from compressed and solidified layers of organic or inorganic matter). Most of Earth's crust is made up of metamorphic rock. Igneous and sedimentary rocks become metamorphic rock as a result of intense heat from magma and pressure from tectonic shifting. Although the rock becomes extremely hot and under a great deal of pressure it does not melt. If the rock melted, the process would result in igneous, not metamorphic rock. Metamorphic alteration of rock causes the texture and/or mineral composition to change. New textures are formed from a process called recrystallization. New minerals (which are simply various combinations of elements) are created when elements recombine.

There are two basic types of metamorphic rock: regional and thermal. Regional metamorphic rock, found mainly in mountainous regions, is formed mainly by pressure, as opposed to heat. Different amounts of pressure produce different types of rock. The greater the pressure, the more drastic the change. Also, the deeper the rock the higher the temperature , which adds to the potential for diverse changes. For example, a pile of mud can turn into shale (a fine-grained sedimentary rock) with relatively low pressure, about 3 mi (5 km) down into the earth. With more pressure and some heat, shale can transform into slate and mica. Metamorphic rock found closer to Earth's surface, or produced by low pressure, characteristically splits or flakes into layers of varying thickness. This is called foliation. Slate is often used as roofing tiles and paving stones. With lots of pressure and increasing heat, rock called schist forms. Schist, which is a medium-grained regional metamorphic rock also has a tendency to split in layers, is subjected to high temperatures, and often contains crystals , such as garnets. Gneiss (pronounced "nice") is formed by a higher pressure and temperature than schist. These rocks are coarse grained and, although layered as schist is, do not split easily. Essentially, metamorphic rocks are made of the same minerals as the original rock or parent rock but the various minerals have been rearranged to make a new rock.

Thermal metamorphic rock, also called contact metamorphic rock, is formed not only by considerable pressure but, more importantly, by intense heat. Imagine molten rock pushing up into Earth's crust. The incredible pressure fills any empty space, every nook and cranny, with molten rock. This intense heat causes the surrounding rock to completely recrystallize. During recrystallization, the chemical composition regroups to form a new rock. An example of this type of thermal metamorphic rock is marble , which is actually limestone whose calcite has recrystallized. Sandstone made mostly of quartz fragments recrystallizes into quartzite. Thermal metamorphic rocks are not as common or plentiful as regional metamorphic rocks. Sometimes a metamorphic rock can become metamorphosed. This is known as polymetamorphism.

See also Metamorphism

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Metamorphic Rock." World of Earth Science. . Encyclopedia.com. 2 Nov. 2018 <https://www.encyclopedia.com>.

"Metamorphic Rock." World of Earth Science. . Encyclopedia.com. (November 2, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/metamorphic-rock

"Metamorphic Rock." World of Earth Science. . Retrieved November 02, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/metamorphic-rock

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

metamorphic rock

metamorphic rock An aggregate of minerals formed by the recrystallization of pre-existing rocks in response to a change of pressure, temperature, or volatile content. Metamorphic rocks can generally be divided into four types: (a) regional metamorphic rocks, formed in response to changes leading to high temperature and high pressure (shearing stress and hydrostatic pressure: see HYDROSTATIC STRESS) accompanying orogenic events (see OROGENY; REGIONAL METAMORPHISM); (b) contact metamorphic rocks, formed in response to changes leading to high temperature (with low pressure) around an igneous intrusion (see THERMAL METAMORPHISM); (c) cataclastic or dynamic metamorphic rocks, formed in response to an increase in directed pressure (shearing stress) particularly in fault and thrust zones (see CATACLASITE); and (d) burial metamorphism, formed in response to changes leading to high pressure (with low temperature).

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"metamorphic rock." A Dictionary of Earth Sciences. . Encyclopedia.com. 2 Nov. 2018 <https://www.encyclopedia.com>.

"metamorphic rock." A Dictionary of Earth Sciences. . Encyclopedia.com. (November 2, 2018). https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/metamorphic-rock

"metamorphic rock." A Dictionary of Earth Sciences. . Retrieved November 02, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/metamorphic-rock

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

metamorphic rock

metamorphic rock Broad class of rocks that have been changed by heat or pressure from their original nature – sedimentary, igneous, or older metamorphic. The changes characteristically involve new crystalline structure, the creation of new minerals, or a radical change of texture. For example, the metamorphic rock slate is made from sedimentary shale.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"metamorphic rock." World Encyclopedia. . Encyclopedia.com. 2 Nov. 2018 <https://www.encyclopedia.com>.

"metamorphic rock." World Encyclopedia. . Encyclopedia.com. (November 2, 2018). https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/metamorphic-rock

"metamorphic rock." World Encyclopedia. . Retrieved November 02, 2018 from Encyclopedia.com: https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/metamorphic-rock

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

metamorphic rock

metamorphic rock An aggregate of minerals formed by the recrystallization of pre-existing rocks in response to a change of pressure, temperature, or volatile content.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"metamorphic rock." A Dictionary of Ecology. . Encyclopedia.com. 2 Nov. 2018 <https://www.encyclopedia.com>.

"metamorphic rock." A Dictionary of Ecology. . Encyclopedia.com. (November 2, 2018). https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/metamorphic-rock-0

"metamorphic rock." A Dictionary of Ecology. . Retrieved November 02, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/metamorphic-rock-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

metamorphic rocks

metamorphic rocks: see rock.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"metamorphic rocks." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 2 Nov. 2018 <https://www.encyclopedia.com>.

"metamorphic rocks." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (November 2, 2018). https://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/metamorphic-rocks

"metamorphic rocks." The Columbia Encyclopedia, 6th ed.. . Retrieved November 02, 2018 from Encyclopedia.com: https://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/metamorphic-rocks

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Metamorphic Rock

Metamorphic Rock

Resources

Metamorphic rock is rock that has changed from one type of rock into another. The word metamorphic (from Greek) means of changing form. Metamorphic rock is produced from igneous rock (rock formed from the cooling and hardening of magma), sedimentary rock (rock formed from compressed and solidified layers of organic or inorganic matter), or existing metamorphic rock. Most of Earths crust is made of metamorphic rock. Igneous and sedimentary rocks are transformed into metamorphic rock as a result of intense heat from magma and pressure from tectonic shifting. Although the rock becomes extremely hot and under a great deal of pressure, it does not melt. If the rock melted, the process would result in igneous, not metamorphic rock. Metamorphism causes the texture and mineral composition to change (although the chemical composition generally remains the same). New textures are formed from a process called recrystallization. New minerals are created when elements recombine.

There are two basic types of metamorphic rock: regional and thermal. Regional metamorphic rock, found mainly in mountainous regions, is formed mainly by pressure, as opposed to heat. Different amounts of pressure produce different types of rock. The greater the pressure, the more drastic the change. Also, the deeper the rock, the higher the temperature, which adds to the potential for diverse changes. For example, mud can lithify into shale (a fine-grained sedimentary rock) with relatively low pressure, about 3 mi (5 km) into Earth. With more pressure and some heat, shale can transform into slate and mica. Metamorphic rock found closer to Earths surface, or produced by low pressure, characteristically splits or flakes into layers of varying thickness. This is called foliation. Slate is often used as roofing tiles and paving stones. With lots of pressure and increasing heat, rock called schist forms. Schist, which is a medium grained regional metamorphic rock also has a tendency to split in layers, is subjected to high temperatures and often contains crystals, such as garnets. Gneiss is formed by a higher pressure and temperature than schist. These rocks are coarse grained and, although layered as schist is, do not split easily. Essentially, metamorphic rocks are made of the same minerals as the original rock or parent rock but the minerals have been recrystallized to make a new rock.

The degree to which metamorphism has progressed, particularly with regard to temperature and pressure, is known as the metamorphic grade. Slate, for example, is a low grade metamorphic rock whereas gneiss is a high grade rock. Metamorphic rocks are also described in terms of facies (a term that means aspect) defined by minerals formed under particular combinations of pressure and temperature.

Thermal metamorphic rock, also called contact metamorphic rock, is formed not only by considerable pressure but, more importantly, by intense heat. Imagine molten rock pushing up into Earths crust. The incredible pressure fills any empty space, every nook and cranny, with molten rock. This intense heat causes the surrounding rock to completely recrystallize. During recrystallization, the chemical composition regroups to form a new rock. An example of this type of thermal metamorphic rock is marble, which is actually limestone whose calcite has recrystallized. Sandstone made mostly of quartz fragments recrystallizes into quartzite. Thermal metamorphic rocks are not as common or plentiful as regional metamorphic rocks. Sometimes a metamorphic rock can become metamorphosed. This is known as polymetamorphism.

See also Rocks.

Resources

BOOKS

Blatt, H., R. Tracy, and B. Owens. Petrology: Igneous, Sedimentary, and Metamorphic. New York: Freeman, 2005.

Fowler, C.M.R. The Solid Earth: An Introduction to Global Geophysics. Cambridge, United Kingdom: Cambridge University Press, 2004.

Tarbuck, E.J., F.K. Lutgens, and D. Tasa. Earth: An Introduction to Physical Geology. Upper Saddle River, NJ: Prentice Hall, 2004.

Christine Miner Minderovic

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Metamorphic Rock." The Gale Encyclopedia of Science. . Encyclopedia.com. 2 Nov. 2018 <https://www.encyclopedia.com>.

"Metamorphic Rock." The Gale Encyclopedia of Science. . Encyclopedia.com. (November 2, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/metamorphic-rock-1

"Metamorphic Rock." The Gale Encyclopedia of Science. . Retrieved November 02, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/metamorphic-rock-1

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Metamorphic Rock

Metamorphic rock

Metamorphic rock is rock that has changed from one type of rock into another. The word metamorphic (from Greek) means "of changing form." Metamorphic rock is produced from either igneous rock (rock formed from the cooling and hardening of magma ) or sedimentary rock (rock formed from compressed and solidified layers of organic or inorganic matter ). Most of Earth's crust is made up of metamorphic rock. Igneous and sedimentary rocks become metamorphic rock as a result of intense heat from magma and pressure from tectonic shifting. Although the rock becomes extremely hot and under a great deal of pressure it does not melt. If the rock melted, the process would result in igneous, not metamorphic rock. "Metamorphism " of rock causes the texture and/or mineral composition to change. New textures are formed from a process called recrystallization. New minerals (which are simply various combinations of elements) are created when elements recombine.

There are two basic types of metamorphic rock: regional and thermal. Regional metamorphic rock, found mainly in mountainous regions, is formed mainly by pressure, as opposed to heat. Different amounts of pressure produce different types of rock. The greater the pressure, the more drastic the change. Also, the deeper the rock the higher the temperature , which adds to the potential for diverse changes. For example, a pile of mud can turn into shale (a fine-grained sedimentary rock) with relatively low pressure, about 3 mi (5 km) into Earth . With more pressure and some heat, shale can transform into slate and mica. Metamorphic rock found closer to Earth's surface, or produced by low pressure, characteristically splits or flakes into layers of varying thickness. This is called foliation. Slate is often used as roofing tiles and paving stones. With lots of pressure and increasing heat, rock called schist forms. Schist, which is a medium grained regional metamorphic rock also has a tendency to split in layers, is subjected to high temperatures and often contains crystals, such as garnets. Gneiss (pronounced "nice") is formed by a higher pressure and temperature than schist. These rocks are coarse grained and, although layered as schist is, do not split easily. Essentially, metamorphic rocks are made of the same minerals as the original rock or "parent" rock but the various minerals have been rearranged to make a new rock.

Thermal metamorphic rock, also called contact metamorphic rock, is formed not only by considerable pressure but, more importantly, by intense heat. Imagine molten rock pushing up into Earth's crust. The incredible pressure fills any empty space , every nook and cranny, with molten rock. This intense heat causes the surrounding rock to completely recrystallize. During recrystallization, the chemical composition "regroups" to form a new rock. An example of this type of thermal metamorphic rock is marble, which is actually limestone whose calcite has recrystallized. Sandstone made mostly of quartz fragments recrystallizes into quartzite. Thermal metamorphic rocks are not as common or plentiful as regional metamorphic rocks. Sometimes a metamorphic rock can become metamorphosed. This is known as polymetamorphism.

See also Rocks.


Resources

books

Dixon, Dougal. The Practical Geologist. New York: Simon & Schuster, Inc., 1992.

Eyewitness: Rocks & Minerals. New York: Alfred A. Knopf, 1988.

Hancock P. L., and B. J. Skinner, eds. The Oxford Companion to the Earth. Oxford: Oxford University Press, 2000.

Keller, E. A. Introduction to Environmental Geology. 2nd ed. Upper Saddle River: Prentice Hall, 2002.

Skinner, Brian J., and Stephen C. Porter. The Dynamic Earth: An Introduction to Physical Geology. 4th ed. John Wiley & Sons, 2000.


Christine Miner Minderovic

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Metamorphic Rock." The Gale Encyclopedia of Science. . Encyclopedia.com. 2 Nov. 2018 <https://www.encyclopedia.com>.

"Metamorphic Rock." The Gale Encyclopedia of Science. . Encyclopedia.com. (November 2, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/metamorphic-rock-0

"Metamorphic Rock." The Gale Encyclopedia of Science. . Retrieved November 02, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/metamorphic-rock-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.