Inside Our Earth : ROCK
·
The earth’s crust is
made up of rocks of various types.
·
A rock is a natural
piece of mineral matter that makes up the earth’s crust.
·
Rocks can be of
differnt:
• Colour
• Texture
• Size
• Colour
• Texture
• Size
Types of Rocks:
• Sedimentary Rocks
• Metamorphic Rocks
Igneous rocks:
·
The word igneous is
derived from the Latin word Ignis which means fire.
·
The rocks formed by
the solidification on the cooling of molten magma, are called igneous rocks.
·
Depending on where the
molten magma cools, they are of the following types:
• Intrusive Rocks
• Extrusive Rocks
• Intrusive Rocks
• Extrusive Rocks
Intrusive Igneous Rocks:
When the molten magma cools
deep inside the earth’s crust,
intrusive igneous rocks are formed. They
• Cool down slowly
• Form large grains
Granite is intrusive igneous rock.
Grinding stones used to prepare paste / powder of spices and grains are made of granite.
• Cool down slowly
• Form large grains
Granite is intrusive igneous rock.
Grinding stones used to prepare paste / powder of spices and grains are made of granite.
Extrusive Igneous Rocks:
·
When the molten magma (lava) comes on the earth’s
surface.
·
it rapidly cools down
and becomes solid.
·
Rocks formed in such a
manner on the crust are called extrusive igneous rocks.
·
They have a very fine grained structure.
·
Basalt is an example
of extrusive igneous rocks.
·
The Deccan Plateau is made up of basalt rocks.
1. These rocks get their name from the Latin word
sedimentum which means settle down.
2. These rocks are formed by the settling down of
sediments.
3. Sediments are the smaller particles /
fragments that are formed by the breaking down of rocks when they roll down,
crack and hit each other.
4. These sediments are transported by wind, water
etc.
5. These sediments; when compressed and hardened;
form sedimentary rocks.
6. Sandstone is an example of sedimentary rock. It is made up of grains of
sand.
7. The sedimentary rocks may also contain fossils
of plants, animals and other micro – organisms that once lived on them.
1. The Greek word ‘metamorphose’ which means change of form, is the root of the word metamorphic.
2. In other words, these are the rocks that are
formed when the igneous and sedimentary rocks change their form under the
following two circumstances:
• Great heat and
• Great pressure
• Great heat and
• Great pressure
3. The following are the examples of metamorphic
rocks:
a. Slate: Clay becomes slate after metamorphosis.
b. Marble: Limestone becomes marble after metamorphosis.
a. Slate: Clay becomes slate after metamorphosis.
b. Marble: Limestone becomes marble after metamorphosis.
Rock Cycle
·
A cyclic manner is
followed in transformation of one type of rock to another type under certain
conditions.
·
This process of
transformation of the rock from one to another is called the rock cycle.
Do You Know?
• The deepest mine (4 km deep) is in South Africa. Engineers have dug a hole about 6 km deep in search of oil.
• A 6000 km deep hole in the ocean floor needs to be dug to reach the centre of the earth (which is not possible!).
• The radius of the earth is 6371 km.
• In the descending order of the volume of the earth (thickness) at its three layers, we first have the core (83 %), then the mantle (16 %) and finally the crust (0.5 %).
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