Metamorphic rocks – Types and Characteristics

Introduction: Metamorphic rocks are formed by the transformation of pre-existing rocks (igneous, sedimentary) to a new type of rock and then followed by the process called metamorphism.

The pre-existing rock is subjected to high temperatures (greater than 150 to 200 °C), and high pressure, which causes physical and chemical changes in the earth’s crust. Example of metamorphic rocks is- Gneiss, marble, slate, schist, etc.

Metamorphic rocks make up a large part of Earth’s crust and form 12% of the Earth’s land surface.

The Process of Metamorphism:

In this process, the rocks transformed into denser, more compact rocks referred to as metamorphic rocks. By rearrangement of components or by reaction with fluids in rocks the new mineral is created. The pressure and temperature can change previously metamorphosed rocks into new types of rocks. The metamorphic rock formed by metamorphosis is squished, smeared out, and folded.

These rocks may be classified as:

  • Common Metamorphic Rocks: Includes phyllite, schist, gneiss, quartzite, and marble.
  • Foliated: Granite and biotite schist, are strongly banded or foliated metamorphic rocks. (Repetitive layering in metamorphic rocks)
  • Non-Foliated Metamorphic Rocks: These rocks do not consist of platy or sheet-like structure. Limestone is not in a flat or elongated shape. Example – marble, quartzite, greenstone, etc.
Types and examples of Metamorphic rocks:
Type of Metamorphic Rocks           Example
Gneiss

It is a very common and widely distributed metamorphic rock. The gneiss is formed due to high temp. and pressure, the result of high-grade regional metamorphism.

Ortho gneiss is gneiss derived from igneous rock. Para gneiss is gneiss are metamorphic rock derived from sedimentary rock.

  • New England, the piedmont, the Adirondacks.
  •  The Rocky Mountains
  •    Australia
  • North Carolina and South Carolina, US, east of the Brevard Shear Zone.
Marble

Marble is formed by the metamorphosis of Limestone. It is produced under the condition of thermal metamorphism.

  •  India
  • Greece
  • Spain
  • Turkey
  • Italy And USA.
Phyllite

It is a cleaved Metamorphic rock having affinities with both slate and mica–schist.

  • Dalradian metasediments of North Western Arran
  • In North Cornwall
Quartzite

Quartzite is an arenaceous rock. It is formed when Quartz rich sandstone or chert has been exposed to high temperature and pressure. In this condition, the quartz grains get fused and a hard, dense irregular rock formation takes place.

  • United States: parts of Pennsylvania, eastern South Dakota, Central Texas, etc.
  • United Kingdom: England, In Wales, Holyhead mountain.
  •  the highest mountain of Mozambique, Mount Binga (2436m)
  • Brazil
Schist

Schist is well foliated, with a higher degree of metamorphism, it is medium to coarse-grained metamorphic rock.

  • Brazil
  • Parts of the Us and Ireland,
  • Australia
Slate

the slate is produced by the low-grade metamorphism of shale. It is a very fine-grained metamorphic rock. Its characteristics are excellent foliation called slaty cleavage.

 

  •  Brazil
  • United Kingdom
  • India
  • China
  • France
  • Spain
  • Portugal

rock cycle- formation of metamorphic rocks.

Characteristics of Metamorphic Rocks:
  • These rocks were once igneous or sedimentary rocks, these are changed or metamorphosed due to intense heat and pressure within the earth’s crust.
  • They are crystalline and often possess foliated textures.
  • After metamorphosis, some rocks become harder than their original forms, such as diamonds from carbon, Quartzite from sandstone, and marble from limestone.
  • The metamorphic rocks don’t contain fossils because the fossils of original sedimentary rocks were destroyed during metamorphosis.
  • These rocks are found in a wide range.
  • The imperfectly foliated are coarse-grained metamorphic rocks. ex. gneisses
  • The fine-grained metamorphic rocks are perfectly foliated. eg. Schist from Shale.
  • Most gneissic metamorphic rocks consisting bands of granular quartz and feldspar.

Usage: 

  • Slates are used in construction, especially as the roof shingle.
  • Some quartzite is used as dimension stones, slabs for flooring, walls, stairs, and for road aggregate.
  • Marble is also used in construction and for sculpture formation.

 

You can also read:

references: https://www.geolsoc.org.uk/ks3/gsl/education/resources/rockcycle/page3459.html

Thank you 🙂

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