Rocks are made up of different minerals. Minerals
are naturally occurring substances which have certain
physical properties and definite chemical composition
Minerals are very important to humankind. Some are
used as fuels. For example, coal, natural gas and
petroleum. They are also used in industries iron.
aluminium, gold, uranium, etc, in medicine, in
fertilisers, etc.
Answers
Answer:
ROCKS AND MINERALS
The earth’s crust is made up of various types of rocks.
Any natural mass of mineral matter that makes up the
earth’s crust is called a rock. Rocks can be of different
colour, size and texture.
There are three major types of rocks: igneous rocks,
sedimentary rocks and metamorphic rocks.
When the molten magma cools, it becomes solid.
Rocks thus formed are called igneous rocks. They are
also called primary rocks. There are two types of igneous
rocks: intrusive rocks and extrusive rocks.
Can you imagine lava coming out from the volcanoes?
Lava is actually fiery red molten magma coming out from
the interior of the earth on its surface. When this molten
lava comes on the earth’s surface, it rapidly cools down
and becomes solid. Rocks formed in such a way on the
crust are called extrusive igneous rocks. They have a
very fine grained structure. For example, basalt. The
Deccan plateau is made up of basalt rocks. Sometimes
the molten magma cools down deep inside the earth’s
crust. Solid rocks so formed are called intrusive igneous
rocks. Since they cool down slowly they form large
grains. Granite is an example of such a rock. Grinding
stones used to prepare paste/powder of spices and grains
are made of granite.
Rocks roll down, crack, and hit each other and are
broken down into small fragments. These smaller particles
are called sediments. These sediments are transported
and deposited by wind, water, etc. These loose
sediments are compressed and hardened to form
layers of rocks. These types of rocks are called
sedimentary rocks. For example, sandstone is
made from grains of sand. These rocks may also
contain fossils of plants, animals and other micro-
organisms that once lived on them.
Igneous and sedimentary rocks can change
into metamorphic rocks under great heat and
pressure (Fig. 2.3). For example, clay changes into
slate and limestone into marble.
Fig. 2.3: Sedimentary rock turned
into a Metamorphic rock
Fossils: The remains
of the dead plants and
animals trapped in
the layers of rocks are
called fossils.
Word Origin
Igneous: Latin word
Ignis meaning fire.
Sedimentary: Latin
word sedimentum
meaning settle down.
Metamorphic: Greek
word metamorphose
meaning change of form.
Do you know?
• The crust forms only
1 per cent of the
volume of the earth,
84 per cent consists
of the mantle and
15 per cent makes
the core.
• The radius of the
earth is 6371 km.
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