Rocks & Minerals | Classifications of Rocks | & Features of Minerals

In this article of Rocks & Minerals we have discussed about the Rocks and minerals & their classification like metallic and non-metallic minerals, also covered features of minerals and also we will study important key points from different types of rocks etc…

Rocks & Minerals | Classifications of Rocks | & Features of Minerals

Table of Content

  • Rocks & Minerals
  • Classification of Rocks
  • Metallic Minerals
  • Non-metallic Minerals
  • Features of Minerals
  • Important Points from Different types of Rocks




Rocks & Minerals


Many people ordinarily think of rock as something hard and stone-like. It is how rock in ordinary language is linked to hardness. ‘Hard like rock’ ‘strong like rock’ are some of the common idioms exemplifying this. But it is interesting to note that ‘silt’ is also a kind of rock. And so are pebbles, sand and soil. Rocks can be hard like granite and soft like clay. Therefore, the natural and solid part of the crust, be it soft like clay or hard like granite, is called rock.


Rocks are of many types. They have been made, or are still in the process of being made in different ways. Rocks may be millions of years old. History of mankind apart, the history of the earth is embedded in rocks. That is why the geologists describe rocks like pages of a book. It is a different story that the language of rocks is different from ordinary language of man. Only few people can understand the language of rocks.


The geographers are interested in rocks from many different angles. The solid part of the earth’s crust is made up of rocks. From the surface of the earth to about 16 km depth 95% of the crust is made up of rocks.


Rocks and Minerals


The rocks and minerals have an intrinsic relationship. Rocks are made of minerals found in solid state. Each mineral is constituted of two or more chemical elements. The whole of the earth is thus made of these minerals. The earth scientists have so far identified about 2000 minerals. Out of these there are twelve common minerals found everywhere on earth. These 12 minerals are rock-forming minerals. Some other special minerals have become essential for industries and modern lifestyles. The common minerals are made up of eight elements found in adequate quantities in nature. About 87% of the minerals found in the earth’s crust are silicates.



Definition of Minerals:Naturally occurring inorganic substance with a definite chemical composition and ordinarily crystalline is called a mineral. Two types of minerals are:


Metallic Minerals

The surface of the metallic minerals is generally slippery and glossy. Gold, copper and lead are metallic minerals. They are melted to obtain metals.


Non-metallic Minerals

Their surface is dull. They cannot reflect the sun-rays. Gypsum, quartz and mica are non-metallic minerals. Metals cannot be obtained from these minerals.


Features of Minerals

(i) Inorganic

(ii) Naturally formed

(iii) Solid

(iv) The internal structure of atomic in them is same

(v) Their chemical composition is similar.



Classification of Rocks

Rocks are chiefly of three types: Igneous, Sedimentary and Metamorphic.


Figure: Rocks Classification



Important Points from Different types of Rocks


(1) The natural and solid part of the crust, whether that be soft rock like limestone or hard rock like granite, is called rock.

(2) 95 per cent of the crust is made up of rocks.

(3) Rocks are made up of minerals.

(4) Around two thousand minerals identified. Out of these 12 are common to all parts of earth and rock-forming.

(5) 87% of the minerals found in the surface of the earth are silicates.

(6) Naturally occurring chemical substances which are solid, inorganic and ordinarily crystalline are called minerals.

(7) Two type of minerals are metallic and non-metallic.

(8) Rocks are of three types igneous, sedimentary, metamorphic.

(9) Igneous are of two types: Extrusive (basalt) and Intrusive (granite, gabro).

(10) Intrusive rocks are of two types: Plutonic (Granite) and Hypabyssal (Dolerite and Pegmatite).

(11) On the basis of their formation igneous rocks are of two types – acidic (granite) and Basic (gabro and basalt).

(12) Igneous rock bodies – Batholith, Laccolith, Stock Sill, Dyke (Dike).

(13) Characteristics of igneous Rocks: Granular, rich in minerals, no folds or layers, no pores, impervious, free of fossils, compact, hard and massive, not easily weathered definite order of crystallisation.

(14) The greatest importance of igneous rocks: quite, rich in minerals, metallic minerals, precious minerals-gold, construction materials, black soil is derived from it.

(15) Sedimentary: Formed from sand, silt, gravel, clay, and pebbles.

(16) Though they are spread over 75% of earth’s surface, they constitute only 5% of the volume of earth’s crust.

(17) Formed in three ways: Inorganic (mechanical) – Loess, Sandstone, Shale, Conglomerate, Braccia. (aeolian, glacial, aqueous, riverine, lacustrine.)

(18) Organic origin: Coal, Limestones, Poly lime. (Carbonaceous, Calcareous.)

(19) Chemically Formed: Rock salt, gypsum and nitrate.

(20) Characteristics of sedimentary rocks: Layered, soft, porous, fossil embedded, without granules or crystals, stratified, plane.

(21) Economic importance: Some minerals – iron ore, phosphate, coal, mineral oil, construction materials, alluvium.

(22) Metamorphic rocks are formed when igneous or sedimentary rocks are wholly or partially changed in their character.

(23) Metamorphism takes place at temperatures ranging from 150°C to 800°C.

(24) Three forms of metamorphism: Dynamic, Thermal and Regional.

(25) Dynamic metamorphism-excessive pressure converts granite to gneiss.

(26) Thermal metamorphism transforms sandstone into quartzite.

(27) Regional metamorphism -Temperature and pressure act together to transform sandstone to quartzite.

(28) Characteristics of Metamorphic rocks: hardness, banded structures and interlocking of crystals, dense and resistant to porosity, form huge masses under mountains.

(29) Economic importance: Construction materials for buildings: industrial uses – beautification materials, asbestos, garnet.

Leave a Comment

error: Content is protected !!