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Solutions for Geography, Class 7, ICSE
What are rocks? Name the main types of rocks with two examples of each.
Rocks are aggregates of one or more minerals, without having a definite chemical composition. The rocks may be composed of hard materials like granite and marble or soft like chalk, clay and sand.
The main types of rocks are:
How are metamorphic rocks formed? Write two characteristics of metamorphic rocks.
When igneous or sedimentary rocks are subjected to excessive heat and pressure inside the earth, changes occur in their colour, hardness, texture and mineral composition. Such changed rocks are called metamorphic rocks.
Two characteristics of metamorphic rocks are:
What is mechanical weathering? How does freezing action of water affect weathering of rocks?
Mechanical weathering involves disintegration of rocks without the change in their chemical composition. It is mainly brought about by:
Freezing action of water — In mountainous regions or in areas with cold climate, the breaking of rocks is caused by the freezing action of water. The cracks and joints in the rocks fill up with water. At night, when the temperature falls, the water in the cracks or joints freezes. The conversion of water into ice increases its volume, thereby requiring more space. This causes widening of cracks and joints and finally leads to their disintegration. This is also called frost action.
Distinguish between oxidation and hydration.
| Sl. No. | Oxidation | Hydration |
|---|---|---|
| 1. | The decomposition of rock in which the minerals present in the rocks react with the atmospheric oxygen present in the rain water is called oxidation. | The disintegration of rocks due to chemical union of water with the minerals present in the rocks is called hydration. |
| 2. | The colour of the rocks change in this process. | The volume of rock increases causing stress which leads to disintegration of the rock. |
Discuss the role of plants and animals in biological weathering.
Role of plants — The penetration of roots in the rock cracks widens the cracks and disintegrates the rocks. The uprooting of trees by winds also breaks the rocks.
Role of animals — Animals such as worms, rabbits and moles dig burrows in the ground. In the process, they loosen the ground and disintegrate the rocks.
What are soil horizons? Name the soil horizons.
The process of soil formation gives rise to four well-marked horizontal layers in the soil profile. These horizontal layers are called soil horizons. The soil horizons are:
The ............... igneous rocks cool below the earth's surface.
The intrusive igneous rocks cool below the earth's surface.
............... metamorphoses into marble.
Limestone metamorphoses into marble.
............... is also known as onion peeling.
Exfoliation is also known as onion peeling.
When water chemically reacts with a mineral, it is called ............... .
When water chemically reacts with a mineral, it is called hydration.
Soil formation is a very ............... process.
Soil formation is a very slow process.
............... is the vertical section of soil from the surface to the parent rock.
Soil profile is the vertical section of soil from the surface to the parent rock.
Rearrange the letters to get the names of the rocks from which these landforms are formed. Then match the landforms with their names.
(a) Pamukkale
(b) Giant's Causeway
(c) The Wave Rock
Igneous rocks are called primary rocks.
Igneous rocks are called primary rocks because these rocks were the first to be formed.
Rocks develop cracks due to change in temperature.
The rocks are heated during the day and cooled during the night. Different minerals present in the rocks expand and contract at different rates according to the changes in temperature. As a result of this unequal expansion and contraction of minerals in the rocks, a series of cracks develop on the outer surface of the rocks.
| Sl. No. | Column A | Column B |
|---|---|---|
| 1. | basalt | soil erosion |
| 2. | fossils | biological weathering |
| 3. | frost action | sedimentary rock |
| 4. | quarrying | soil conservation |
| 5. | deforestation | mechanical weathering |
| 6. | crop rotation | igneous rock |
| Sl. No. | Column A | Column B |
|---|---|---|
| 1. | basalt | igneous rock |
| 2. | fossils | sedimentary rock |
| 3. | frost action | mechanical weathering |
| 4. | quarrying | biological weathering |
| 5. | deforestation | soil erosion |
| 6. | crop rotation | soil conservation |
Soil is found in the (atmosphere/lithosphere).
Lithosphere
Name two types of igneous rocks
Two types of igneous rocks are:
Sandstone is an example of ............... rocks.
Sandstone is an example of sedimentary rocks.
Excessive heat and pressure change granite into gneiss. True or False?
True
Mention two uses of rocks.
Two uses of rocks are:
The decay of rocks as a result of chemical action is called (decomposition/disintegration).
The decay of rocks as a result of chemical action is called decomposition.
Name two factors that affect weathering.
Two factors affecting weathering are:
Granular disintegration is caused due to change in temperature. True or False?
True
Name the different types of chemical weathering.
The different types of chemical weathering are:
..............., ............... and ............... are responsible for biological weathering.
Plants, animals and human activities are responsible for biological weathering.
The rocks which are formed from magma are called ............... rocks.
igneous
Quartzite is ............... rock.
a metamorphic
Which of these is not a type of weathering?
geological
Carbonic acid disintegrates limestone as a result of
carbonation
Which of these factors is not responsible for soil formation?
deforestation
Which of these factors is responsible for soil erosion?
overgrazing