Page 103 - SST Class 07

material is called the magma. This molten material which cools down under the earth’s crust takes a
acts like solid because of extreme pressure. long time and forms crystals of larger size.
Quiz Time Igneous extrusion
(lava)
Fill in the blanks :

1. The material that forms the crust of the earth is
Igneous
called ___________ . intrusion
2. The core can be divided into two parts—the
___________ and the ___________ .
3. The inside of the earth is made of
___________ .

4. ___________ is the thinnest of all layers. Formation of igneous rocks
5. The two chief elements in the continental crust Just Think!
are ___________ and ___________ .
When it is so hot inside the earth, then how some
ROCKS
places are so cold on its surface, such as
The material that forms the crust of the earth is Greenland?
called rock . By rock is meant harder materials like
Igneous rocks are called primary rocks because
granite, sandstone and marble and some softer
other types of rocks are formed from these. These
materials like chalk, clay, sand etc. rocks are economically important as they are the
source of many important minerals, such as iron,
nickel, copper, lead, zinc, gold and platinum.
Also, these rocks are useful in construction.

Sedimentary Rocks
You have read that all other rocks are formed from
Granite Sandstone Chalk igneous rocks. The igneous rocks break and erode
The rocks in the earth’s crust can be classified into into sediments due to the movement of water, ice
three types—igneous rocks , sedimentary rocks and and wind, and are carried to the new places by
metamorphic rocks . these agents. These sediments deposit on the
floors of the seas, rivers and lakes, layer upon
Igneous Rocks layer. They are pressed and hardened by their
There is molten material, called magma, in the own weight. The rocks formed in this manner are
earth’s inside which comes out through holes, called sedimentary rocks , such as sandstone,
called volcanoes . When this magma comes out on limestone, slate etc.
the earth’s surface, it is called lava . It is very hot Erosion : Particles
carried away from
when it is inside the earth, but when it comes out their source by
on the earth’s surface, it cools down quickly and water or wind. Deposition : Particles
deposited as loosely
packed sediment.
turns into solid rocks. The rocks which come out
on the earth’s surface are called extrusive rocks , Compaction : Particles
such as basalt. We can find these in the Deccan squeezed together
under great pressure.
Plateau in southern India. Sometimes the magma
cools down under the earth’s crust and changes Key Increasing Cementation : Particles
pressure glued together as
into rocks, such rocks are called intrusive rocks , mineral solutions
harden.
such as granite, basalt, diorite etc. The magma
Formation of sedimentary rocks
Inside the Earth
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