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Granite and Gabbro are the two main examples of the igneous rocks.

There are five main types of rocks on the basis of agents of formation: 

1. Riverine Rocks These are formed by the sediments deposited by running water or river. 

2. Lacustrine Rocks These are formed by the deposition of silt etc on the bed of lakes. 

3. Glacial Rocks These are formed by the debris carried on and deposited by glaciers. 

4. Aeolean Rocks These are formed by the deposition sand accumulation by the wind. 

5. Marine Rocks These are formed by the deposition of sediments at the ocean floor. These types are Calcarious and Carbonaceous sedimentary Rocks.

Igneous rocks are the first to be formed on the earth’s surface, due to which, they are significantly important. 

The importance of these rocks is presented through the following points:

1. Abundant minerals are found in these rocks. Minerals like gold, silver, zinc, copper, sulphur, magnesite etc. are found in these rocks. 

2. These rocks are the primary rocks, thus, other rocks have been formed from them. 

3. The processes of weathering and erosion have their effect on these rocks. Due to this reason, the black soil has been formed from them. 

4. The stones/rocks obtained from these rocks are useful for the work of constructing buildings. 

5. Due to the fertile soil produced by these rocks, they are beneficial from the agricultural perspective. 

6. The surface water filters through these rocks and goes inside. Thus, these rocks are important in enhancing groundwater purity.

Igneous rocks are classified on the basis of the formation-place and chemical composition.

The following are the features of igneous rocks: 

1. There is a lack of layers in igneous rocks. 

2. These rocks are non-porous. 

3. These rocks are crystallized. 

4. Fossils are not found in these rocks. 

5. These rocks are extremely hard. 

6. The effect of physical weathering on these rocks is greater in amount compared to chemical weathering. 

7. Metallic minerals are found in these rocks.

On the basis of chemical composition igneous rocks may be classified into two groups i.e. Acid igneous rocks and Basic igneous rocks. Acid rocks have silica content 65-85 percent e.g. granite which is made up of large crystals of quartz, feldspar and mica. Basic rocks contain high percentage oxides of denser material, silica content is between 40-60 percent with a density of 2.8 g/cm3 and 3.0 g/cm3. Acid rocks are lighter than Basic rocks.

The dead sea abounds in chemically formed sedimentary rock because the evaporation of water from it is rapid.

Rain water, wind, ice or the running water are the agents involved in the formation of sedimentary rocks. These agents break and carry on loose material and deposit it in various low lying areas to convert into the solid sedimentary rocks. (c) Chemically-formed sedimentary rocks are produced through evaporation of water from solutions containing minerals. In this ways a rock like ‘gypsum’ is produced. Other examples are nitrates and potash etc.

Three types of rocks are found on the earth’s surface – igneous rocks, sedimentary rocks and metamorphic rocks.

The igneous rocks were the first to be formed. They form the basis of formation of other types of rocks. Thus, they are called primary rocks.

• Volcanic activity and other earth movements constantly take place on the earth.
• While these are occurring, the igneous and sedimentary rocks in that region are subjected to tremendous pressure and heat.
• This leads to changes in nature as well as the chemical composition of the original rocks.

There are three types of sedimentary rocks on the basis of the nature of sediments, their origin, composition and mode of formation. These are mechanically-formed sedimentary rocks, organically formed sedimentary rocks and chemically- formed sedimentary rocks.

Rocks which are formed when the hot and fluid magma and lava cooled down and solidified at the time of formation of the earth are called the Igneous Rocks. These rocks are the first to be formed, thus, they are also called the Primary Rocks. After these rocks only, other rocks have been formed.

i. Hill in ‘A’ is made up of soils and rocks.

ii. In ’B’, the process of digging is shown. The land is dug and the rocks and soil that is extracted is loaded in to a truck.

iii. In ‘C’ we see pebbles and rocks of different types, shapes, colours, etc.

iv. Yes, these are all pictures of naturally occurring processes on land leading to rock and soil formation.

v. We use things shown in A and C for construction purposes; coloured pebbles are used for decoration.

The buried remains of dead animals or plants embedded in the rocks and preserved petrified form are called fossils.

(i) Hillforts in Maharashtra are old quarry sites from which stone or other materials have been extracted for the construction of the fort and other buildings.

(ii) In the pits and dugouts left behind after rock extraction, water was allowed to accumulate and these lakes, banks, etc., were created.

(iii) Therefore, most of the hill forts in Maharashtra have lakes or elephant yards.

When the molten material, known as magma within the crust and lava on the surface cools down, it solidifies giving rise to igneous rocks.

i. lithosphere

ii. three

iii. Igneous

iv. Sedimentary

v. Igneous

i. Granite

ii. Mining

iii. Igneous rock

iv. Basalt

v. Sedimentary

vi. Metamorphic

vii. diamond

viii. Laterite

i. True

ii. False

As Igneous rocks are formed out of the material from the interior of the earth, these rocks are also referred to as primary rocks.

• Moving streams are so powerful that it can wear away soil rocks.
• Rocks on higher land get eroded due to the strong current of the streams and they in turn get carried away into the sea.
• Silt too is brought down from the mountain top from where the streams originate.
• Most of the sand in the river is silt carried by the streams and the weather material from inland rocks transported by the streams.
• The moving of soil and rock with the stream, termed as erosion can be summed up as the cause of sand formation in a river.

Fossils are remains of vegetation and animals buried under the sediments. The sedimentary rocks are stratified rocks and are found in layers. These fossils are preserved in between these layers. But in Igneous rocks, the fossils are destroyed due to high temperature of lava.

i. Marble, Slate.

ii. Granite and Basalt.

i. Laterite.

ii. Metamorphic rocks.

i. False

ii. True

Correct Answer is: (c) Igneous

i. True

ii. false

i. Shale, corals.

ii. Metamorphic and Igneous rock

Laccoliths is formed by the intrusion of magma in the erupting channel just below the crust. Batholiths are deep seated dome shaped formation of magma intrusion, generally forming the base of mountain ranges, e.g., Ranchi Batholiths.

These are the fuels accumulated between two impermeable layers of the sedimentary rocks, e.g. peat, coal and petroleum etc.

It is the process of turning the loose material into hard rock, which helps in the formation of the sedimentary rocks found in different layers one upon another.

It is the process of transformation of sedimentary and igneous rocks into metamorphic rocks through extreme temperature and compression by volcanism and diatrophism by physical and Chemical changes.

Metamorphism is a process of transformation of sedimentary and igneous rocks into the metamorphic rocks through physical and chemical reactions. Main causes are great temperature and pressure beneath the earth’s crust, which changes the original texture and form of the rocks into dense, crystalline and fine grained rocks.

Metamorphic rocks are composed of fine particles and dense, smooth material. These are very precious rocks, particularly for building stones like marble, garnet, slate quartzite etc.

Metamorphic rocks are heavy and hard.

The term metamorphism means change of form. It may be physical or chemical or both.

Metamorphic rocks are those rocks which were formerly igneous or sedimentary rocks, but owing to extreme heat and pressure in the interior of the earth it has been changed or altered to such an extent that they are quite different from what they once were slate, which is in reality clay, and marble’ which is in reality lime stone. Other examples of metamorphic rocks are quartzite from sand stone, graphite from coal, gneiss from granite and Mica from Schist.

Thermal metamorphism : When the transformation of the original rock takes place principally because of the influence of high temperature, the rock is said to be caused through Thermal metamorphism. For example, graphite (from coal) and slate (from clay). The heat may result from the intrusion of hot magma or from the friction of moving rock layers. It may also occur due to chemical changes. Dynamic metamorphism : When the transformation of the original rock takes place mainly because of the influence of pressure at a great depth within the earth’s crust, it is known as Dynamic Metamorphism.

Regional metamorphism When metamorphism of bed rocks takes place over a very large area, it is called Regional metamorphism. It is usually caused by the movement of the earth’s crust. Contact metamorphism when it takes place over a small area, it is called Local Metamorphism or Contact Metamorphism. It commonly occurs when hot magma comes in contact with other rocks