Class 3 Science Chapter 18 Rocks and Minerals

A mineral is a naturally occurring substance, a chemical composition that has a characteristic and specific physical properties such as habit and streak. All rocks are made up of substances called minerals.

1. Igneous Rocks
2. Sedimentary Rocks
3. Metamorphic Rocks

These rocks are formed from molten rock material or when the hot liquid mineral comes from deep inside the earth. It comes out through cracks on the earth’s surface and then cools down to form the rocks. These rocks contain minerals such as mica and quartz. They also contain silica, magnesium, and iron. Granite and Pumice are the two important types of igneous rocks.

Water, wind and snow carry with them small pieces of gravels and pebbles. They are deposited on the surface of the soil and gradually get covered with many layers of the soil.

These rocks are formed through action of heat and pressure of the soil. Slate and marbles are the typical examples of such rocks.

Minerals are another very important natural resource. They occur in the rocks of the earth’s surface. Most minerals are mined, that is, they are taken out by digging large, deep holes called mines in the earth. Minerals are used as metal and fuels.

Most metal occur as ore or a mixture of metal and earth. They have to be refined before they can be used. Some important minerals found in India are iron, coal, copper, manganese, zinc, Aluminium, mica and gold.

Metals are used to make machines, bridges, cars, aeroplanes, trains, tools and utensils.

Among mineral fuels, the most important are coal, petroleum and natural gas. coal is burnt in homes and used to drive railway engines and run machines. It is used to heat water to produce steam. Once coal was called the black gold because of its various uses. Petroleum is used to drive machines, trains and almost all kinds of vehicles. It is often called the liquid gold. Natural gas is used in homes as cooking gas. Compressed natural gas (CNG) is used to drive vehicles. It is a pollution-free fuel. Most vehicles in Delhi and Mumbai make use of CNG these days.

Mineral deposits are limited. They cannot last forever. So, we must use them carefully. There are ways through which we can conserve minerals.
1. We should use bicycles to go for short distances;
2. Many neighbours can go to their offices in a single vehicle;
3. We should use alternative sources of energy such as the sun, wind, water and earth.
4. These are permanent sources of energy. They will last forever. The most important advantage of these sources is that they give us pollution-free energy.

Air, water and sunlight are essential for good health. These are nature’s gifts to the human. Man has made these gifts unfit with his activities. The huge amount of smoke and harmful gases coming out from vehicles, factories, power plants, aeroplanes and atomic explosions pollute air and water.

1. Sedimentary rocks are formed from sediments.
2. Igneous or sedimentary rocks changes into metamorphic rocks.
3. Coal is formed from dead plants.
4. Petroleum is formed from dead animals.
5. The earth is made up of rocks.

1. Coal was once called the black gold.
2. CNG is a good fuel.
3. Minerals are renewable.
4. Granite and pumice are igneous rocks.

Answers:
1. True
2. True
3. False
4. True

Coal and petroleum product are called fossil fuels because these are formed millions year ago from dead animals and plants.

Earth is made of rock and soil.

There are three types of rocks:
1. Igneous Rocks
2. Sedimentary Rocks
3. Metamorphic Rocks