Have you ever wondered how plants are grown and what is the main factor for plant growth? Yes, the soil is one of the most important factors for plant growth, along with water, minerals, sunlight, etc. How is soil formed? We can see many tiny rocks in the soil. How are rocks formed? Soil is formed due to the weathering of rocks.
The rocks are formed due to natural calamities like a volcanic eruption, accumulation of sediments for a long time, etc. The Earth’s topmost layer is made up of rocks and soil. Rocks are the outer solid layer of the Earth’s crust. Different types of rocks are made up of various types of minerals. The study of rocks is called Petrology. Read on more to know about rocks and the types of rocks, and their formation, weathering of rocks, ores, and minerals in the article below.

What are Rocks?

Rocks are the supporting bases of the Earth’s crust. Solid minerals are deposited on it in large quantities. The most abundant element is oxygen which is present in a combined state with silica in the form of silicate rocks. The earliest rocks on Earth assembled about 3.8 billion years ago as a collection of minerals that have not been consequently broken down by erosion or melted. Rocks are naturally occurring solid substances that are combined with one or more minerals. The Earth layer lithosphere is mainly composed of different rocks.

Classification or Types of Rocks

Based on the conditions under which rocks are formed, they are classified into three types, namely igneous rocks, sedimentary rocks, and metamorphic rocks.

Fig: Rock Cycle

(a) Igneous Rocks: Rocks formed by the solidification of volcanic eruptions are called Igneous rocks. Igneous, meaning “fire,” refers to the solidification of the Earth’s internal molten magma.

Formation: Igneous rocks are formed by cooling molten rocks. The hot liquid rock that lies below the Earth’s crust is known as magma. The hot magma is pushed upward by the pressure of the other rocks. Some of it cools and hardens below the Earth’s crust, and some of it flows above the Earth’s crust. The magma that reaches the Earth’s crust and flows out is called lava.

Examples:
1. Basalt: Basalt is an igneous rock formed by lava cooling on the Earth’s surface. It has fine grains.

Fig: Basalt

2. Granite: The most common igneous rock on the Earth’s surface is granite. It is very hard and is used for making buildings, statues and for paving streets.

Fig: Granite

3. Pumice: Pumice is a light-colored igneous rock. It is thrown out during volcanic eruptions. Dentists use pumice for polishing teeth. It is also used as a body scrubber.

Fig: Pumice

(b) Sedimentary Rocks: Rocks formed by the accumulation of sediments and compression of the lower layers over long periods of time are called sedimentary rocks.

Formation: These rocks are formed by the accumulation of sediments. These sediments are generally the broken rock particles brought down by streams and rivers in the form of mud, pebbles, gravel, and sand.

1. They are deposited on the beds of rivers and oceans. The heavier particles (like stones and pebbles) settle down. First, the light particles (like sand and silt) settle down next, and the lightest particles (like clay) settle down finally.
2. Those particles which settle down are called sediments. So, the sediments are deposited in layers. All the time, fresh layers of sediments are piled over the previous ones.
3. The weight of the top layers presses down the lower layers, which in due course of time, are hardened to form rocks.

Examples:

1. Sandstone: It may be yellow, brown, pink, or red in colour. It is often used in making buildings. The red fort in Delhi is made up of red sandstone.

Fig: Sandstone

2. Limestone: Limestone is formed from the remains of animals and plants. Chalk is one form of limestone. Limestone is formed from the shells and skeletons of millions of tiny sea or ocean creatures.

Fig: Limestone

3. Shale: It is made up of clay and mud particles. Shale is a smooth sedimentary rock. It is used to make bricks and tiles.

Fig: Shale

(c) Metamorphic Rocks: Rocks formed by the transformation of igneous or sedimentary rocks into different kinds of rocks under heat and pressure are called metamorphic rocks. In the intense heat and pressure, the minerals that form the sedimentary and igneous rocks change their compositions, forming new minerals. This transforms or morphs the existing rocks into a new kind of rock with a new structure and texture. These morphed rocks are called metamorphic rocks.

Formation: These rocks are formed by alteration of the existing rocks by heat, pressure, etc. These are altered forms of igneous and sedimentary rocks under very high pressure and heat, making the rocks hard and compact.

Examples:

1. Slate: It is a metamorphic rock formed from shale. It splits easily into thin slices. It is grey and shiny. It is used to make blackboards and slates. It is also used for making roof tiles in hilly areas.

Fig: Slate

2. Gneiss: It has light and dark bands. It is used in making statues.

Fig: Gneiss

3. Marble: It is formed by the metamorphosis of limestone. The taj mahal is made up of white marble.

Fig: Marble

Uses of Rocks

Rocks and minerals are useful in many ways:
1. As Building Materials: Marble, slates, stones, etc., are used for making buildings. Granite rock is used for building dams and roads.
2. As Decorative Materials: Beautiful carvings and statues made from stones are used for decoration.
3. As Ornaments: All the precious stones (diamonds, rubies, emeralds, etc.) are obtained from rocks. These stones are used in ornaments.
4. Gemstones are the most prized and famous of all minerals. They are prized because they have beauty, durability, and rarity.
5. As Fertilisers: Minerals are added as fertilizers in the soil to get a good crop. Nitrate, phosphate, sulphate, and potassium are good minerals for the growth of plants.

What is Weathering?

Weathering is an action of elements of weather and climate over earth materials. The factors such as wind, water, temperature change, etc., break down rocks, and the flowing water carries weathering rock particles and deposits them over plains.
Weathering can also be defined as the mechanical disintegration and chemical decomposition of rocks through the actions of various elements of weather and climate.
As very little or no motion of materials takes place in weathering, it is an in-situ or on-site process.

Types of Weathering

Weathering processes are conditioned by many complex topographic, geological, climatic, and vegetative factors. Not only do the weathering processes differ from climate to climate, but also the depth of the weathering mantle.
There are three major types of weathering processes and they are chemical, physical or mechanical, and biological weathering processes.

(a) Chemical Weathering: A group of weathering processes viz; hydration, oxidation, solution, carbonation, and reduction act the rocks to dissolve, decompose, or reduce them to a fine clastic segments state through chemical reactions by oxygen, topside, and/or soil water and other acids.

1. In addition to the carbon dioxide present in the air, the decomposition of animals and plants raises the quantity of carbon dioxide underground.

(b) Physical/Mechanical Weathering: Physical weathering processes rely upon some external forces. Expansion forces may be caused due to temperature changes, crystal growth, or animal activity. Water pressures are controlled by drying and wetting cycles.

1. The multiple of these forces is applied both at the top of the surface and within different earth materials leading to rock crack.
2. The particular processes are slow and small but can cause great harm to the rocks because of continued wash out the rocks suffer due to repetition of expansion and contraction.

(c) Biological Weathering: Biological weathering is the benefaction to or elimination of minerals and ions from the weathering environment and physical changes due to the movement or growth of organisms.

1. Wedging and burrowing by organisms like rodents, earthworms, termites, etc., help in proving the new surfaces to chemical attack and assists in the penetration of air and moisture.
2. Human beings by disturbing cultivating soils, ploughing, and vegetation also help in mixing and creating new contacts between water, minerals, and air in the earth materials.
3. Decaying animal and plant matter helps in the production of carbonic, humic, and other acids that enhance solubility and decay of some elements.
4. Plant roots apply enormous pressure on the Earth’s materials, automatically breaking them apart.

What are Ores?

The minerals from which metals can be recovered are called ores. Bauxite and magnetite are examples of ores. Ores are deposited that contain one or more minerals, usually metals. Minerals are divided into metals and non-metals. In India, the non-metallic minerals are mainly dolomite and gypsum.

Difference Between Minerals and Ores

Minerals	Ores
Naturally occurring substances of metals present in the Earth’s crust are called minerals.	Minerals that can be used to obtain the metal profitably are called ores.
All minerals are not ores.	All ores are essential minerals.
They have a definite crystalline structure. Examples: Common salt, lime, chalk, etc.	They do not have a definite crystalline structure. Examples: Haematite, copper pyrites, malachite, etc.

Soil Erosion

Eroding or removal of top fertile soil due to various agents like wind, water, and even human activities is soil erosion. Soil erosion results in a continuous loss of topsoil, ecological degradation, soil collapse, etc., worsening due to human activities such as construction, grazing, agriculture, deforestation, etc. It is a continuous process that occurs either slowly that continues relatively unnoticed, or can occur at an alarming rate.

Summary

Rocks are the hardest part of the Earth’s crust. There are 3 major types of rocks- igneous, sedimentary, and metamorphic rocks. They are formed due to various natural processes like volcanic eruptions, due to sun temperature, pressure, wind, etc., and few are formed due to the deposition of sediments from the ages. Basalt, shale, slate, limestone, marble, sandstone, etc., are few examples of igneous, sedimentary, and metamorphic rocks.
Rocks are used to construct and decorate many buildings; few rocks are used to make jewellery, etc. Breaking up rocks is called weathering. Due to weathering, the soil is formed. There are 3 types of weathering: biological, physical, and chemical weathering. Minerals are mostly found in rocks as crystals. Some of the minerals are used for extracting metals like copper, gold, iron, silver, etc., that contain such a mineral called ore. Both rocks and minerals are useful in many ways.

Frequently Asked Questions (FAQs) on Rocks: Types, Weathering of Rocks and Ores

Q.1. What are the 2 types of weathering?
Ans: Physical/Mechanical and chemical weathering are the 2 types of weathering.

Q.2. How do rocks turn into soil?
Ans: Soil is formed due to weathering of rocks. Rocks are broken down due to sun, wind, and rain.

Q.3. Which is the hardest type of rock?
Ans: Diamond is the hardest type of rock.

Q.4. What is the difference between soil and rock?
Ans: Rocks are the hardest part of the Earth’s surface, whereas soil is formed due to the weathering of rocks.

Q.5. Which is the softest rock?
Ans: Talc is the softest rock on the Earth.

Study About Soil Types Here

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