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Mafic Rocks

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What is Meant by Mafic Rocks?

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The Earth, by weight, mostly consists of mafic or ultramafic rocks, but silicic rocks are considered to be more abundant on the surface of the Earth. The common type of mafic rocks is basalt, pyroxene, biotite, etc. In this article, we will talk about this type of rock. We will learn about what are mafic rocks, mafic minerals, their meaning, definitions, features, and examples, etc. This topic will be helpful to understand one of the types of igneous rocks which are formed from magma and which we usually study in Geography, Geography, Earth Sciences, Physical Geography, etc.

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Introduction

Rocks are said to be the hard matter which forms after the solidification of the magma and because of various other geographical phenomena. These are generally of three main types which include igneous rocks, sedimentary rocks, and metamorphic rocks. Among these, igneous rocks are said to be the primary rocks because they occur first and then sedimentary rocks form and then the formation of metamorphic rocks happens because of geological processes on the above two types of rocks. If we talk about Igneous rocks, these are formed after the solidification of magma and can be of two types i.e. Intrusive and Extrusive. These are being divided on the basis of where they actually occur. If rock formation is done below the surface of the Earth is known as intrusive igneous whereas if it occurs above the surface of the Earth, it is known as Extrusive rocks. Mafic rock is an example of Intrusive igneous rock.


Meaning of Mafic

It is a portmanteau term that is made up of magnesium and ferric. On the basis of silica content, igneous rocks can be classified into various types. Silica is found in abundance in igneous rocks because of which is considered the basis of classification. On this basis, igneous rocks can be divided into four major types i.e felsic, intermediate, mafic, and ultramafic ( written as per the silica content in decreasing order). Mafic is a kind of igneous rock which are rich in magnesium and iron. This type of rock contain 45 to 55 % silica content and 4 mafic igneous rocks minerals are pyroxene, amphibole, olivine, and mica. Mafic word is sometimes also used as a synonym for dark coloured minerals. 

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Definitions

Some of the standard definitions are given below:

  • "In Geology, of or relating to rocks rich in dark, ferromagnesian minerals." - dictionary

  • "Mafic describes rocks containing more dark-coloured substances and iron than other rocks." - Cambridge dictionary.

  • "It is Relating to or denoting a group of dark-coloured, mainly ferromagnesian minerals such as pyroxene and olivine and often contrasted with felsic. ( Geology ). - Lexico definition.

  • "Mafic is a collective term for minerals present in igneous rocks Or "relating to igneous rocks or silicate minerals." Or "( Geology ) of or pertaining to igneous rocks that are rich in dark-coloured minerals and that contain magnesium and iron and a comparatively low level of silica." - Collins Dictionary.

Features

The basic features of mafic rocks are given below:

  • This is one of the important types of igneous rocks that are classified on the basis of silica content.

  • It is a type of rock that crystallizes from silicate minerals at high temperatures. Sometimes, these rocks are also called basaltic. 

  • Olivine, pyroxene, amphibole, and biotite are common rock-forming minerals of mafic.

  • Common examples of mafic rocks are basalt, gabbro, diabase, etc.

  • They are dark in colour ( whereas felsic rocks are light in colour).

  • Chemically, these rocks are consist of magnesium, iron, and calcium.

  • Mafic magma has a low content of silica because of which before cooling, mafic lava has a low viscosity.

  • The volcanic eruptions consist of mafic lava are less explosively violent as compared to felsic volcanic eruptions.

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Additional Information

On the basis of the texture of rocks, different names of mafic rocks are given below in the table:

Different Names of Mafic Rocks

Texture

Name of Mafic Rocks

Pegmatitic

Gabbro pegmatite

Coarse grained - Phaneritic

Gabbro

Coarse grained - Porphyritic

Porphyritic Gabbro

Fine grained - aphanitic

Basalt

Fine grained - Porphyritic

Porphyritic basalt

Puroclastic

Basalt tuff or breccia

Vesicular

Vesicular basalt

Amygdaloidal

Amygdaloidal basalt

Small vesicles

Scoria

Glassy

Tachylyte, Sideromelane, and Palagonite


Conclusion

To sum up we can say that mafic is a term which is made up of magnesium and ferric thus used to describe the rocks which are rich in two whereas now it is also used to describe the igneous rocks which are rich in high content of magnesium as well as iron. It is a dark coloured rock that consists of silica content less than felsic and intermediate whereas more than ultramafic igneous rocks. On the basis of the texture of the rocks, different names of mafic rocks can be there. This topic is useful to study whenever we talk about igneous rocks and their types.

FAQ (Frequently Asked Questions)

Question1. What do You Mean by Mafic Rocks?

Answer. Mafic rocks are those types of igneous rocks that consist of magnesium as well as iron. When we divide the igneous rocks on the basis of silica content, mafic rocks stand at 3rd rank in terms of it i.e 45 to 55% silica content and they are dark colour rocks in which most common mafic minerals are Olivine, pyroxene, amphibole, and biotite.

Question2. What are the Characteristics of Mafic Rocks?

Answer. This is one of the important types if we igneous rocks are classified on the basis of silica content and it contains 45 to 55% of silica. It is a type of rock that crystallizes at high temperatures from the silicate minerals. Olivine, pyroxene, amphibole, and biotite are considered to be common rock-forming mafic minerals. They are dark in colour and these rocks are consist of magnesium, iron, and calcium. Mafic magma has a low content of silica because of which before cooling, thus, mafic lava has a low viscosity.

Question3. What are Mafic and Felsic Rocks?

Answer. Mafic and felsic rocks are both an important type of igneous rocks which are being classified on the basis of silica content present in them. Where mafic contains 45 to 55% of silica content, the latter contains more than 65% of silica content. The former is dark coloured whereas the latter is an example of light colour rocks. The examples of the former rock are gabbro, basalt, etc and of the latter are rhyolite, granite, etc.