Metamorphic Rocks

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Metamorphic Meaning

Metamorphic basically means ‘change to form’.

In nature, many metamorphic things have gone through some kind of transformation or change.

In Latin, META means ‘from,’ and in Greek means ‘to transform,’ MORPH in Greek means ‘form.’

Therefore, the name metamorphic comes from Greek words meaning “change of shape”.

According to Geology, the term metamorphic is denoted to the rock that undergoes metamorphism. They are formed when igneous, sedimentary, or other metamorphic rocks undergo physical transformations under very great heat, pressure or due to other natural agencies. 

Metamorphic rocks are formed, buried inside the Earth’s surface on being subjected to high temperatures and pressures of the rock layers above it.


Metamorphic Definition

In Geology, metamorphic basically pertains to or exhibiting structural change or transformations.

Metamorphic rock used to be some other kind of rock; however, due to sudden changes in an environment, it changed into another form inside the earth. 

They were once igneous or sedimentary rocks;, however, they have been changed (metamorphosed) when subjected to intense heat and pressure within the Earth's crust.

They are crystalline by nature and often have a “squashed” (foliated or banded) texture.


Metamorphic Rocks Examples

They are formed when other rocks are affected by great temperatures and pressures. Metamorphic rocks do not melt, but the chemicals they contain may change their forms or crystal shapes. 

Examples of metamorphic rocks:

  1. Marble

  2. Slate  

  3. Granite gneiss and biotite schist are strongly banded and foliated.

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Types of Metamorphic Rocks

The metamorphic rocks are foliated and non-foliated as well.

The word ‘foliation’ comes from the Latin word ‘foulm,’ which means ‘leaf,’ referring to the sheet-like planar structure.

There are two main types of metamorphic rocks:

Foliation in geology refers to a repetitive layering in metamorphic rocks. Each layer can be as thin as a sheet of paper, and over a meter in thickness.

  1. Foliated Rocks: Foliated rocks are formed in an environment with directed pressure and shear stress.

  2. Non-foliated Rocks: Non-foliated rocks are formed in an environment without a directed pressure or relatively near to the surface with very little pressure.


Types of Metamorphism

Five types of metamorphic rock formation can be understood by the three ways by which metamorphic rocks can be formed.

So, the five types of metamorphism is discussed below:

  1. Contact Metamorphism

  2. Regional Metamorphism

  3. Dynamic Metamorphism 

  4. Burial Metamorphism

  5. Hydrothermal Metamorphism


Characteristics of Metamorphic Rock

Characteristics of metamorphic rocks are discussed hereunder:

  1. Contact Metamorphism: The contact metamorphism occurs when magma comes in contact with an already existing body of rock.

In this type of metamorphism, we can rocks changes, mainly because of high heat in a relatively small region.

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  1. Regional Metamorphism: Regional metamorphism occurs when rocks are buried deep in the Earth’s crust. A type of metamorphism in which the texture of the rock is chamged by an excessive heat and pressure over a wide area or region.

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  1. Dynamic Metamorphism: A type of metamorphism also known as cataclasis. It is formed mainly because of a mechanical deformation with little long-term temperature change. 

The textures of rocks are constituted in such adjustments ranging from breccias poised of angular, tattered rock pieces to very fine-grained, granulated or powdered rocks with apparent foliation and lineation.

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Diagram: Dynamic metamorphism

Basically, contact and regional metamorphism differ in both area and pressure involved.

  1. Hydrothermal Metamorphism: This metamorphism is the result of extensive interaction of rock with high-temperature fluids. Therefore, the difference in composition between the existing rock and the invading fluid drives the chemical reactions. 

The hydrothermal fluid may originate from a magma that enters nearby and cause fluid to circulate in the nearby crust, from circulating hot groundwater, or from ocean water. 

If the fluid brings in substantial amounts of ions into the rock and withdraws substantial amounts of ions from it, the fluid has metasomatized the rock—changed its chemical composition.

  1. Burial Metamorphism: It is the lowest form of metamorphism that occurs to rocks buried deep in sediments to depths that exceed the conditions in which sedimentary rocks form.

When rocks undergo burial metamorphism, they encounter a uniform stress of lithostatic pressure, and do not develop foliation. 

The main type of mineral that usually grows during this metamorphism is zeolite, which is a group of low-density silicate minerals. 

Generally, a strong microscope is required to see the small-sized minerals of zeolite grains.

  1. Pressure: Normal stress pushes together rock in one direction, i.e., in the direction of maximum stress. Simultaneously, in a perpendicular direction, the rock undergoes stretching in the direction of minimum stress. 

The shear stress pushes on side of a rock in a parallel direction, while the other end is compressed in an opposite direction.

FAQ (Frequently Asked Questions)

Q1: What are some examples of Metamorphic Rocks?

Ans: There are two types of metamorphic rocks:

  1. Foliated Rocks: Examples: Slate, schist, amphibolite, gneiss, migmatite, phyllite, etc.

  2. Non-foliated Rocks: Examples: Amphibolite, quartzite, marble, hornfels, etc.

Q2: Write uses of Metamorphic Rocks in everyday life.

Ans: Quartzite and marbles are most commonly used metamorphic rocks in our day-to-day life.  The marbles are available in a collection of different colors that were deformed into coils while the rock was ductile. The marbles are often used mostly as a decorative stone in buildings and some marbles are considered a better quality stone, carved into statues, however, they lack in variety of colors.

Q3: Write some examples of Sedimentary Rocks.

Ans: The examples of sedimentary rocks are:

A. Clastic Sedimentary Rocks: These rocks are from mechanical weathering rubble.

  1. Breccia

  2. Conglomerate

  3. Stale

  4. Slit

  5. Sandstone

B. Chemical Sedimentary Rocks:  They are formed when dissolved minerals precipitate from the solution.

  1. Rock salt

  2. Chert

  3. Iron ore

  4. Flint

  5. Limestone

  6. Dolomites

Q4: What minerals are found in the Metamorphic Rock?

Ans: Common minerals in metamorphic rocks are: quartz, feldspar, mica, calcite, and hornblende. 

Index minerals in metamorphic rocks determine how much rock material was metamorphosed or transformed into another form. It is also called the grade of metamorphism.

Index minerals include the following:

  1. Chlorite

  2. Garnet

  3. Epidote

  4. Staurolite

  5. Kyanite

  6. Sillimanite