Classify the Rocks and Describe their Composition, Characteristics, and Usage.

Classification of rocks

There are many types of rocks. Based on the basic nature and origin of construction, they are divided into three classes-

1. Igneous rocks,

2. Sedimentary rocks,

3. Metamorphic rocks.


(1) Igneous rocks

These are the primary rocks of the earth’s crust, which were formed when the earth’s molten material cooled down. They were formed in the past when there were no animals and plants, so their remains are not visible in these rocks. They were the first to form on Earth, yet not all igneous rocks are the oldest. Due to the eruption of the volcano, the formation process of these rocks continues even today. But other rocks have certainly been formed from these. Therefore, it is better to call igneous rocks primary rocks. characteristics of igneous rocks

They are hard and sticky which are formed when the liquid cools down. These raves live in different sizes, forms, and sequences. Water cannot enter these, which is why chemical changes do not take place in them, but physical disintegration is more. Their fission is easily done by the action of sun heat, and snow water.

They have a place of deposition, but the joints are affected by erosion and weathering. They are compact and do not have layers. The illusion of layering occurs in igneous rocks due to the occurrence of a joint on the plane in the rocks and the re-deposition of another layer of lava on one layer of lava. Animal remains are also not found in them. These rocks are easily eroded. igneous rocks Classification is done on various grounds. Among these, their position and structure are important.

Types of Igneous Rocks based on Location

1. Intrusive Rocks – There are molten substances in the inner part of the earth which are called magma. Their average temperature is 5950 centigrade. When they solidify slowly, large deposits are formed and it takes more time to form such rocks. These types of rocks are called intrusive igneous rocks. Typical examples of these are granite and gravestone rock. These rocks come out only after the upliftment or erosion of the earth’s surface. These rocks located at greater depths are called finite styles. They are named after the word ‘Pluto’ which means ‘underworld’.

2. Intermediate rock- When the internal liquid material is unable to reach the surface while coming out, then it freezes in the form of a vertical wall, bridge, and dam between the sedimentary rocks of the path. These are called liths and they make right angles with the layers of the earth’s surface. These rocks are harder and stronger than the rocks that the lava entered. That is why on the surface of a country lava walls are found in the form of walls or ranges. Lava rock is found in the Singhbhum district of Bihar, which is famous for the name of the latest dolerite. In the United States of North America, the stamped or ring wall is known as the Cleveland lava wall.

3. Extrusive Rocks – When molten rocks solidify on the earth’s surface, they do not form rocks due to rapid cooling, it is called extrusive igneous rocks. Generally, during the eruption of a volcano, molten material comes out on the surface, which is called lava. slag rock is Also called volcanic rock. Lava coming out of the joints has banked a wide part of the surface because due to fluidity it flows like coal tar. Many such lava flows have formed the northwest cover in India and the Columbia Plateau of America. Lava is like glass. An example of this is obsidian.

Types of Igneous Rocks based on Composition

The chemical composition of igneous rocks varies. In these, there is a mixture of constituent elements in different amounts, but in all rocks, there is a mixture of silica in a small amount. Silica is a type of hard stone from which gas is prepared. Based on composition, igneous rocks are divided into two classes-

1. Supersilicic rocks, 

2. Hyposilicic rocks.

1. Supersilicic Rocks – In these rocks, the amount of silica is up to 80 percent. These are available in the upper layer of the earth. Due to the deficiency of iron and magnesium, their color becomes yellow and faded. Generally, there is an abundance of crystals and feldspar in them. Due to the solid body form, the supersilicic rocks are simple and are less affected by the process of erosion, which is why they are used in the construction of buildings.

2. Micro-silicic rocks The amount of silica in the composition of these rocks is up to 52 percent. Iron oxide, lime, and aluminum predominate in these. There is absolutely no alkaline substance in it. The amount of sand and silica in these is less, due to which their color is deep and black. They are found in the marginal part of the earth. Although these rocks melt at higher temperatures than granite rocks. But they are thinner than they are. These are more affected by seasonal action, basalt is a simple example of this. Rocks are found more in oceanic volcanic regions and islands.

Apart from this, two categories can also be made – 

(a) Secondary igneous rocks – In these, the amount of silica ranges from 55% to 65%. oxide The main rock is. 

(b) Very low silica igneous rocks- These have less than 45% silica content. Puedolites are the main rocks. The economic importance of igneous rocks is mineral deposits. The larcenous shield of North America is rich in valuable minerals like gold, iron, copper, etc. There are gold and diamond mines in the Western Plateau of Australia and South Africa.

(2) Sedimentary rocks

Deposits of soil, pebbles, and stones transferred by water, wind, and ice are formed on the earth’s surface in the form of clay, these are called sedimentary rocks. These are small and large particles of different sizes and types. They are made of rock, in which the remains of those animals and plants are found, which have fallen between the layers during the formation period. They are spread over three-fourths of the earth’s surface, but their sum in the composition of the earth’s surface is only 5 percent. These are most important for mankind. In the formation of sedimentary rocks, there is an abundance of crystal, clay, and lime. Its rock-powders are made of various chemicals and organic elements. These rocks are classified on different basis goes. Among them, their method of composition and place of origin is important.

Types of sedimentary rocks based on the method of formation:

1. Rocks made from erosional powder or non-living rocks – are deposited by taking rock powder from one place to another by abductors. The rocks formed in this way are pulverized rocks. Most of the rocks in the world fall into this category. There are two classes of them—(a) sandy rocks and (b) clayey rocks

(a) Sandy rocks- In these rocks, crystal mineral predominates. As a result, they turn into sand and gravel. Due to fine particles of clay, lime, and silica, hard and different-sized particles of sand harden and become rock. (b) Clayey Rocks – These are the rocks formed by the deposition of minute particles of soil. clay content in

It is high, in which white sugar, chloride, and aluminum are part. So these rocks are soft but they are impregnable.

2. Rocks made of chemicals- Flowing water takes away some soluble elements with it. These chemical substances get frozen there when there is no water. The heavier particles settle in the lower layers and the lighter ones in the upper layers and thus rocks are formed. These types of rocks are Shalkhari or Gypsum, Rock Salt, Sessile, and Ankara. 3. Rocks made of organic elements or animal rocks – components of animals and plants gradually: –

Gradually they get accumulated and turn into hard rocks. Some of them are high in lime and some have carbon

(a) Calcareous Rocks – Calcareous rocks have a high amount of lime and are formed by organisms-

It is made from the skeletons of animals and the remains of plants. These rocks are found more in the shallow seas of tropical and temperate zones. Limestone, dolomite, and limestone are these types of rocks. (b) Carbon-dominated rocks: Carbon-dominated rocks are made from the remains of plants and trees. Carbon element is present in more quantity in these. As a result of heat and pressure, the modified form of the plant becomes a mineral. Coal and oil-bearing rocks are similar types of rocks. 

Types of sedimentary rocks based on place of origin

1. Continental Rocks: The rocks formed by air in desert and coastal regions are called sedimentary rocks. Their layers are less organized and rigid. Their particles are round and smooth. Their color is red. Sandstone and clay come under this category. 2. Marine rocks – These rocks are formed in the shallow parts of the sea. These three categories are sandstone, Shale, and Limestone.

Economic Importance of Sedimentary Rocks Sedimentary rocks is valuable for human life. Coal and mineral oil which today provide power and

The pillars of civilization are the product of these rocks. Lime and chalk make cement and sand makes glass. Sandstone is used in building construction. Metals like gold, tin, and copper are also found in these rocks. Due to this, the house is available for human residence, food grains for food, and power for industries. Smelting furnaces are made from fire clay metals. Salt, manure, and nitrogen are obtained from them.

(3) metamorphic rocks

The form and properties of igneous and sedimentary rocks change due to heat, pressure, and earth movement. These types of rocks become harder. Mineral elements also get transformed and their specialties also become new. The original condition of the rocks remains, but after the complete transformation, it becomes difficult to identify the original form, and often the rocks become coarse. The universal form of metamorphic fields is the parallelepiped arrangement of crystals. This type of texture is given the noun of scaling. This process of transformation is called metamorphosis. Altered shale is available in mountainous regions. For this reason, their expansion is less than the sedimentary style.

Economic Importance of Rocks Rocks is important substances for human life. Human life gets more than 2000 things from rocks and through them. Most of the coal is obtained from rocks. Earth’s mountain-building movements suppress large forests with soil through earthquakes and other outbreaks. Then after hundreds of years, they turn into coal. Building stones, industrial minerals, coal, iron, oil, etc., and precious metals, gold, silver, etc. are obtained from rocks. The upper crust of the entire earth, on which man is settled, is made up of fine powder of rocks.

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