Chapter 7 - Rocks and Rock Types
(A) How is sand that flows in a river formed? Collect some information about where the sand comes from.
Ans: As the river flows, mainly originating from the mountains, it collects various rocks as well as sediments. These particles are also carried away along with the river water. As the river flows with high energy and speed, the particles are gradually destroyed into smaller particles through forces such as water, wind, and gravity. As these rocks hit the floor or hit against each other, they are broken into smaller pieces. These soil particles are transported by the flowing river to the low-lying areas and are deposited there as sand.
(B) Which of the following monuments are built in igneous rock?
(1) The Taj Mahal
(2) Fort Raigad
(3) The Red Fort
(4) Ellora Sculpture
Ans: Ellora Sculpture
Explanation: Igneous rocks form when hot, molten rock crystallises and solidifies. The Ellora Sculptures, located in Maharashtra, are a World Heritage Site which is famous for rock-cut architecture and art work cutting across various religions. They are made of basalt rock, which is a formation of volcanic eruption. Therefore, Ellora’s sculpture is made of igneous rocks.
(C) Find the differences between –
(1) Igneous and sedimentary rocks
Ans:
| Sr No | Igneous rocks | Sedimentary rocks |
|---|---|---|
1 | When the molten material, known as magma within the crust and lava on the surface, cools down, it solidifies giving rise to rocks. These are known as igneous rocks. | Due to weathering, rocks are broken up into small pieces after which they get deposited and form very thin layers that become harder over a long period of time. This leads to development of sedimentary rocks. |
2 | Igneous rocks are hard, heavy and homogeneous. | Sedimentary rocks are generally brittle and lightweight. |
3 | Basalt, granite, pumice, etc. are igneous rocks. | Sandstone, limestone, corals, etc. are sedimentary rocks. |
(2) Sedimentary and metamorphic rocks
Ans:
| Sr No | Sedimentary rocks | Metamorphic rocks |
|---|---|---|
1 | Due to weathering, rocks are broken up into small pieces after which they get deposited and form very thin layers that become harder over a long period of time. This leads to development of sedimentary rocks. | Metamorphic rocks are formed when other pre-existing rocks like igneous and sedimentary rocks go through chemical and physical changes due to heat and pressure. |
2 | Sedimentary rocks are generally brittle and lightweight. | Metamorphic rocks are hard, heavy and recrystallised. |
3 | Sandstone, limestone, corals, etc. are sedimentary rocks. | Marble, diamond, slate, etc. are metamorphic rocks |
(3) Igneous and metamorphic rocks
Ans:
| Sr No | Igneous rocks | Metamorphic rocks |
|---|---|---|
1 | When the molten material, known as magma within the crust and lava on the surface, cools down, it solidifies giving rise to rocks. These are known as igneous rocks. | Metamorphic rocks are formed when other pre-existing rocks like igneous and sedimentary rocks go through chemical and physical changes due to heat and pressure. |
2 | Igneous rocks are hard, heavy and homogeneous. | Metamorphic rocks are hard, heavy and recrystallised. |
3 | Basalt, granite, pumice, etc. are igneous rocks. | Marble, diamond, slate, etc. are metamorphic rocks. |
(D) Which types of rocks are predominantly found at the following locations?
(1) Central Maharashtra
Ans: Basalt.
(2) South Konkan
Ans: Granite and Laterite.
(3) Vidarbha
Ans: Granite, Basalt and sedimentary rocks.