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They are aggregates or physical mixture of one or more Minerals. Minerals on the other hand are made up of two or more Elements in a definite ratio. They have a definite chemical composition. Crust is made up of more than 2000 minerals, but out of these, 6 are the most abundant and contribute the maximum to this uppermost part of the earth. These are feldspar, quartz, pyroxenes, amphiboles, mica and olivine.
Rocks are of immense economic importance to us.
Rocks differ in their properties, size of particles and mode of formation. On the basis of mode of formation rocks may be grouped into three types:
(a) Igneous
(b) Sedimentary and
(c) Metamorphic
Igneous Rocks
Igneous Rocks are formed by crystallization from a liquid, or magma. They include two types
Volcanic or extrusive igneous rocks form when the magma cools and crystallizes on the surface of the Earth
Intrusive or plutonic igneous rocks wherein the magma crystallizes at depth in the Earth.
Magma is a mixture of liquid rock, crystals, and gas. Characterized by a wide range of chemical compositions, with high temperature, and properties of a liquid.
On the basis of their mode of occurrence, igneous rocks can be classified as : extrusive or volcanic rocks and intrusive rocks.
(i) Extrusive igneous rocks are formed by cooling of lava on the earth’s surface. As lava cools very rapidly on coming out of the hot Interior Of The Earth, the mineral crystals forming these rocks are very fine. These rocks are also called volcanic rocks. Gabbro and basalt are very common examples of such rocks. These rocks are found in volcanic areas. Deccan plateau’s regur Soil in India is derived from lava.
(ii) Intrusive igneous rocks are formed when magma solidifies below the earth’s surface. The rate of cooling below the earth’ s surface is very slow which gives rise to formation of large crystals in the rocks. Deep seated intrusive rocks are termed as plutonic rocks and shallow depth intrusive rocks are termed as hypabyssal. Granite and dolerite are common examples of intru- sive rocks. From this point of view, therefore, igneous rocks can, in accor- dance with their mode of formation, be classified as (a) Plutonic, (b) Hyp- abyssal and (c) Volcanic rockmasses. The huge blocks of coarse granitic rocks are found both in the Himalaya and the Decean Plateau.
Sedimentary Rocks
Sedimentary Rocks are formed by successive deposition of sediments. These sediments may be the debris eroded from any previously existing rock which may be igneous rock, metamorphic or old sedimentary rock. Sedimentary rocks have layered or stratified structure. The thickness of strata varies from few millimeters to several metres. So these rocks are also called stratified rocks. Generally, these rocks have some type of fossil between their strata. Fossil is the solid part or an impression of a prehistoric animal or plant embedded in strata of sedimentary rocks. Sedimentary rocks are widely spread on the earth surface but to a shallow depth.
The formation of sedimentary rocks involves five processes:
- Weathering – The first step is transforming solid rock into smaller fragments or dissolved ions by physical and Chemical Weathering as discussed in the last lecture.
2. Erosion – Erosion is actually many process which act together to lower the surface of the earth. In terms of producing sediment, erosion begins the Transpiration process by moving the weathered products from their original location. This can take place by gravity (mass wasting events like landslides or rock falls), by running water. by wind, or by moving ice. Erosion overlaps with transpiration.
3. Transportation – Sediment can be transported by sliding down slopes, being picked up by the wind, or by being carried by running water in streams, rivers, or ocean currents. The distance the sediment is transported and the energy of the transporting medium all leave clues in the final sediment that tell us something about the mode of transportation.
4. Deposition – Sediment is deposited when the energy of the transporting medium becomes too low to continue the transport process. In other words, if the velocity of the transporting medium becomes too low to transport sediment, the sediment will fall out and become deposited. The final sediment thus reflects the energy of the transporting medium.
5. Lithification (Diagenesis) – Lithification is the process that turns sediment into rock. The first stage of the process is compaction. Compaction occurs as the weight of the overlying material increases. Compaction forces the grains closer together, reducing pore space and eliminating some of the contained water. Some of this water may carry mineral components in solution, and these constituents may later precipitate as new minerals in the pore spaces. This causes cementation, which will then start to bind the individual .
Metamorphic rocks are formed under the influence of heat or pressure on sedimentary or igneous rocks. Tremendous pressure and high temperature change the colour, hard- ness, structure and composition of all types of pre-existing rocks. The process which bring about the change is known as Metamorphism and the ultimate products, formed due to operation of such processes are defined as the Metamrphic rocks.
Metamorphism refers to the changes in mineral assemblage and texture that result from subjecting a rock to pressures and temperatures different from those under which the rock originally formed.
The original rock that has undergone metamorphism is called the protolith. Protolith can be any type of rock .
Metamorphism occurs because rocks undergo changes in temperature and pressure and may be subjected to differential Stress and hydrothermal fluids. Metamorphism occurs because some minerals are stable only under certain conditions of pressure and temperature. When pressure and temperature change, chemical reactions occur to cause the minerals in the rock to change to an assemblage that is stable at the new pressure and temperature conditions. But, the process is complicated by such things as how the pressure is applied, the time over which the rock is subjected to the higher pressure and temperature, and whether or not there is a fluid phase present during metamorphism. Different types of metamorphic rocks are found all over the world. In India, marble is found in Rajasthan, Bihar and Madhya Pradesh, whereas slates are available in plenty in Orissa, Andhra Pradesh and Haryana. In Kangra and Kumaun regions ]of Himalaya, slates of different colours are found.,
Rocks are the building blocks of the Earth’s crust. They are made up of minerals, which are naturally occurring, inorganic solids with a definite chemical composition and crystal structure. Rocks are classified into three main types: igneous, sedimentary, and metamorphic.
Igneous rocks are formed when magma or lava cools and solidifies. Magma is molten rock that is found beneath the Earth’s surface. Lava is magma that has reached the Earth’s surface. When magma or lava cools, it crystallizes into minerals. The type of igneous rock that forms depends on the composition of the magma or lava and the rate at which it cools.
Igneous rocks can be classified into two main types: intrusive and extrusive. Intrusive igneous rocks form when magma cools and crystallizes beneath the Earth’s surface. Extrusive igneous rocks form when lava cools and crystallizes on the Earth’s surface.
Intrusive igneous rocks are typically coarse-grained, while extrusive igneous rocks are typically fine-grained. This is because intrusive igneous rocks have time to cool slowly and crystallize at depth, while extrusive igneous rocks cool quickly at the Earth’s surface.
Sedimentary rocks are formed when pieces of other rocks are broken down and then deposited and compacted. The pieces of rock that form sedimentary rocks are called sediment. Sediment can be transported by water, wind, or ice. When sediment is deposited, it is compacted and cemented together to form sedimentary rock.
Sedimentary rocks can be classified into three main types: clastic, chemical, and organic. Clastic sedimentary rocks are formed when pieces of other rocks are broken down and then transported and deposited. Chemical sedimentary rocks are formed when minerals precipitate out of water. Organic sedimentary rocks are formed from the remains of Plants or animals.
Metamorphic rocks are formed when existing rocks are subjected to heat and pressure. The heat and pressure cause the minerals in the rock to change their shape and form new minerals. Metamorphic rocks can be classified into two main types: foliated and non-foliated. Foliated metamorphic rocks have a layered appearance, while non-foliated metamorphic rocks do not.
The type of metamorphic rock that forms depends on the type of rock that is being metamorphosed, the amount of heat and pressure that is applied, and the duration of the metamorphism.
Igneous, sedimentary, and metamorphic rocks are the three main Types of Rocks. They are formed in different ways and have different properties. Igneous rocks are formed when magma or lava cools and solidifies. Sedimentary rocks are formed when pieces of other rocks are broken down and then deposited and compacted. Metamorphic rocks are formed when existing rocks are subjected to heat and pressure.
What are the three main types of rocks?
The three main types of rocks are igneous, sedimentary, and metamorphic.
- Igneous rocks are formed when magma or lava cools and solidifies.
- Sedimentary rocks are formed when pieces of other rocks are broken down and then cemented together.
- Metamorphic rocks are formed when existing rocks are subjected to heat and pressure.
What are the characteristics of igneous rocks?
Igneous rocks are formed when magma or lava cools and solidifies. Magma is molten rock that is found beneath the Earth’s surface. Lava is magma that has reached the Earth’s surface. Igneous rocks are classified based on their texture and composition.
- The texture of an igneous rock refers to the size and shape of the crystals that make up the rock.
- The composition of an igneous rock refers to the minerals that make up the rock.
What are the characteristics of sedimentary rocks?
Sedimentary rocks are formed when pieces of other rocks are broken down and then cemented together. The pieces of rock can be pieces of igneous rocks, sedimentary rocks, or metamorphic rocks. The cementing material can be minerals, organic matter, or water. Sedimentary rocks are classified based on their texture, composition, and depositional Environment.
- The texture of a sedimentary rock refers to the size and shape of the particles that make up the rock.
- The composition of a sedimentary rock refers to the minerals that make up the rock.
- The depositional environment of a sedimentary rock refers to the place where the rock was formed.
What are the characteristics of metamorphic rocks?
Metamorphic rocks are formed when existing rocks are subjected to heat and pressure. The heat and pressure can cause the rocks to change their texture, composition, and mineral content. Metamorphic rocks are classified based on their texture, composition, and metamorphic grade.
- The texture of a metamorphic rock refers to the size and shape of the crystals that make up the rock.
- The composition of a metamorphic rock refers to the minerals that make up the rock.
- The metamorphic grade of a metamorphic rock refers to the amount of heat and pressure that the rock has been subjected to.
Question 1
Which of the following is not a type of rock?
(A) Igneous
(B) Sedimentary
(C) Metamorphic
(D) Volcanic
Answer
(D) Volcanic is not a type of rock. It is a type of eruption.
Question 2
Igneous rocks are formed when:
(A) Lava cools and solidifies
(B) Sediments are compacted and cemented together
(C) Existing rocks are changed under heat and pressure
(D) All of the above
Answer
(A) Igneous rocks are formed when lava cools and solidifies.
Question 3
Sedimentary rocks are formed when:
(A) Lava cools and solidifies
(B) Sediments are compacted and cemented together
(C) Existing rocks are changed under heat and pressure
(D) None of the above
Answer
(B) Sedimentary rocks are formed when sediments are compacted and cemented together.
Question 4
Metamorphic rocks are formed when:
(A) Lava cools and solidifies
(B) Sediments are compacted and cemented together
(C) Existing rocks are changed under heat and pressure
(D) All of the above
Answer
(C) Metamorphic rocks are formed when existing rocks are changed under heat and pressure.
Question 5
Which of the following is an example of an igneous rock?
(A) Granite
(B) Sandstone
(C) Marble
(D) Shale
Answer
(A) Granite is an example of an igneous rock.
Question 6
Which of the following is an example of a sedimentary rock?
(A) Granite
(B) Sandstone
(C) Marble
(D) Shale
Answer
(B) Sandstone is an example of a sedimentary rock.
Question 7
Which of the following is an example of a metamorphic rock?
(A) Granite
(B) Sandstone
(C) Marble
(D) Shale
Answer
(C) Marble is an example of a metamorphic rock.
Question 8
Igneous rocks are typically:
(A) Hard and dense
(B) Soft and porous
(C) Brittle and easily broken
(D) None of the above
Answer
(A) Igneous rocks are typically hard and dense.
Question 9
Sedimentary rocks are typically:
(A) Hard and dense
(B) Soft and porous
(C) Brittle and easily broken
(D) None of the above
Answer
(B) Sedimentary rocks are typically soft and porous.
Question 10
Metamorphic rocks are typically:
(A) Hard and dense
(B) Soft and porous
(C) Brittle and easily broken
(D) None of the above
Answer
(A) Metamorphic rocks are typically hard and dense.