Definition of Rocks
A rock can be defined as total minerals. Sometimes single or whole types of minerals, such as rock salt and lime, are more common than two or more different minerals.(Class 11 Geography Chapter 2 Notes)
Rocks have been used as tools, since the Stone Age, Of course, the development of ancient civilization is linked to rocks again.
Rock is a naturally occurring compound that combines one or more minerals. The outer solid layer of the Earth is made up of lithosphere rocks (lithosphere means rocks).
A rock may be composed of a single element or mineral and in the name of that element or mineral, they are formed.
The shape of the rocks varies and their properties may be hard or soft. A minute big stone and sand particle both called rocks.
They can be as hard as granite and as soft as graphite. They cannot recover as lime and as slate. Earth’s crust is made up of 2000 minerals, but the most important of all 20 minerals.
Also read this: Class 12 Geography Chapter 1 Notes
Types of Rocks
The Rocks are made up of different types of “minerals”. They can be soft or hard and come in many colors. On the basis of structure and appearance, rocks can be divided into three groups:
(1) Igneous Rocks
(2) Sedimentary Rocks
(3) Metamorphic Rocks
1. Igneous Rocks :
The word “Igneous” is derived from the Latin word “ignis”, that means ‘fire’. These rocks are formed by sedimentation and cooling lava and magma. They can be crystalline or non-crystalline.
They are also called primitive rocks because they are the oldest rocks. At first, the Earth was in hot and molten form. Ignition rocks are formed by magma or volcanic cooling and aggregation.
It can form on the surface of the earth or on the surface of the earth’s crust. There are over 700 igneous rocks, most of which are found underground of earth.
After the eruption in the soft and weak parts of the Earth, the volcano emits gases. After the lava cooled and consolidated, flammable rocks formed.
(Class 11 Geography Chapter 2 Notes)
Classification of Igneous Rocks :
Where, why and under what conditions, lava has a cooling and integration process, which plays an important role in the formation of igneous rocks.
For example, a slow cooling process results in a harder grain structure and faster cooling with a better grain structure on one side. All this leads to the formation of different types of ignition rocks.
It is generally divided into two parts:
1. Extrusive Igneous Rocks
2. Intrusive Igneous Rocks
Extrusive Igneous Rocks :
These rocks are formed by cooling molten magma on the surface of the Earth. When the molten magma comes out of the Earth’s surface, the existing gases evaporate at a rapid rate, causing the molten magma to spread to the Earth, such as shielding and cooling.
Intrusive Igneous Rocks :
These rocks from magma, which cools and freezes in the crust of the planet. These are intensely ignited rocks.
We categorize these stones into two more types.
(a) Plutonic rocks
These rocks formed deep in the earth.
(b) Hypabyssal rocks.
They sell magma rising below the Earth’s surface by ‘cracking’ and cooling into joints, ie not deep plutonic rocks.
Characteristics of Igneous Rocks :
1. These rocks are formed by lava and conjugation, so most of the minerals are found in such rock. Iron, nickel, magnesium, copper, zinc, chromite, diamond, mica, and platinum are abundant in these rocks.
2. These are hard rocks and have no layer.
3. Most of these rocks are crystalline, but as the volcano cools rapidly, these rocks acquire crystalline properties.
4. They are located in vertical and horizontal shapes.
5. About 85 percent of the Earth’s surface is made up of igneous rocks.
6. The composition of these rocks depends on the process of cooling the lava.
7. They do not have a lot of holes and water does not serve such stones, so they are used for construction purposes.Â
Also read this: Class 9 Geography Chapter 2 Notes
(Class 11 Geography Chapter 2 Notes)
Sedimentary Rocks
Sedimentary rocks are formed by minerals and organic particles formed or formed by weathering and weathering in a resource area and then transported to remove water, air, ice, mass movements, or ice. It is also known as Strat Rocks.
The lower layers of these rocks consist of larger pieces, while the upper layer is made into a composite shape of smaller size.
Based on their development, they are divided into the following areas:
1. Clastic Rocks:
The word ‘clastic’ is derived from the Greek word “Klastose”, meaning ‘broken part’. These rocks are part of the original rock and are formed by time-consuming processes that break the rocks into pebbles, sand, or mud pebbles and expose them to the wind, snow, and water.
These can be further classified into:
2. Mechanically Formed Sedimentary Rocks :
Soft rocks, sand grains, clays, or Mud soils strengthen the layers over time, and these soft rocks shrink and take shape with the help of cementing agents such as calcite or silica. Sandstone, Shell, breccia and conglomerate.
The conglomerate is located on Mount. Kailash, Talchir, and Shivalik Hills near Chandigarh. In other words, these are rocks formed by the accumulation of material from other rocks compressed by cement.
(Class 11 Geography Chapter 2 Notes)
3. Organic Rock:
These rocks from the remains of plants and animals. When these remains are buried for a long time, they change their shape turns to a different form.
It is a continuous process with the help of heat and pressure, resulting in the formation of organic rocks. Beet coal is a classic example of organic rocks that are formed with little change in the remains of plants and animals, so it is of little use.
Good quality organic rocks are formed over a long period of time. Bituminous and Lignite (coal) are the best quality organic rocks when the remains of plants and animals are buried for a long time and their appearance changes considerably. We also get petroleum from organic rocks.
Characteristics of Sedimentary Rocks :
1. Fossils are found in rocks.
2. These stones have layers.
3. These rocks have holes and water can easily pass through them.
4. These rocks do not contain crystals like welded rocks.
5. They are not as hard as-welded rocks, so they rot easily.
6. Examples of these rocks are the Himalayas in Asia, the Western Cordillera in North America, the Alps in Europe, and the Andes in South America. Examples of these rocks In India is the Ganges-Brahmaputra plain.
7. These rocks are a source of oil, coal, and natural gas.
8. Sedimentary rocks have sprouts called ‘Ripples’ because they are brittle. The deltas of Mahanadi, Godavari, Krishna, and Kaveri are examples of such stones.
9. pebble-like stones are tied into two types by some cement agents (i) Corgolomerate: They are formed from circular stones (ii) Breccia. They are formed from angular stones.
(Class 11 Geography Chapter 2 Notes)
Metamorphic Rocks
The word “metamorphic” comes from the Greek word ‘metamorphosis’, meaning ‘change’.
The process of making these rocks takes place at a depth of 12 to 16 kilometers from the Earth’s surface. The chemical and physical shape of sedimentary and igneous rocks changes due to the internal heat of the Earth, the pressure of the layers of rock on them, and the interaction of different materials.
There are three types of metamorphic rocks known as metamorphism processes:
1. Dynamic Metamorphosis:
The process of ‘changing’ due to acute pressure is known as dynamic metamorphism.
2. Thermal/Contact Metamorphism :
This process is caused by intense heat present in the interior of the Earth. The stones formed in this process are called Thermal/contact metamorphic stones.
3. Regional Metamorphism :
The rocks formed by this process are called regional metamorphic rocks because the process of transformation at many places due to contraction and friction is called Regional Metamorphism.
7. Many famous buildings in Agra like Marble, Tughlakabad Fort, Agra Fort and Delhi’s Red Fort are built with these stones. Graphite is used for pencils and crosses. It is located in Orissa and Andhra Pradesh.
Characteristics of Metamorphic Rocks :
1. The transition process is caused by heat, pressure, and friction.
2. Some metamorphic rocks are stronger and harder than their original stones. Marble and quartz made of limestone and sandstone that make up the erosion process are very difficult for them.
3. They can be obtained from any type of rock.
4. They are available in various colors.
5. Concise stone is used for construction and quartzite for ‘glass making’.
6. Precious stones like diamond, ruby, sapphire are found in these stones.
7. Many famous buildings in Agra like Tajmahal by using Marble, Tughlakabad Fort, Agra Fort and Delhi’s Red Fort are built with these stones. Graphite is used for pencils and crosses. It is located in Orissa and Andhra Pradesh.
(Class 11 Geography Chapter 2 Notes)