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ROCK SYSTEM:
ü Rocks
are a type of minerals.
ü Rocks
are the solid substances that are present in the interior surface of the earth.
ü Minerals:
Earth composed of various kinds of elements. Mineral has definite composition
and a definite atomic structure.
ü 98%
of earth crust is composed of 8 elements.
v Oxygen
v Silicon
v Aluminum
v Iron
v Calcium
v Sodium
v Potassium
v Magnesium
ü When
elements are combined they are called Minerals.
ü Element
+ element = Minerals
ü The
basic source of all minerals is magma in the earth.
ü When
magma cools down the minerals occur in sequence called Rocks.
ü Mineral
+ Mineral = Rock
ü Rocks
may be hard (granite) or soft (sandstone).
ü Rocks
may be of different colors. (Gabbro – Black and Quartz – milky white).
The
rocks are of 3 types depending on their origin, structure or chemical
properties.
ü Igneous
ü Sedimentary
ü Metamorphic
IGNEOUS ROCKS:
 |
| IGNEOUS ROCK |
ü
Ignis means Fire.
ü
When the molten magma
cools it becomes solid.
ü
These are called
igneous rocks.
ü
The igneous rocks are
forming since the formation of the earth.
ü
These were the first to
be formed.
ü
These are called
v
Primary rocks.
Or
v
Parent rocks.
Or
v
Volcanic rocks.
Or
v
Massive rocks.
ü
By erosion the igneous
rock becomes sedimentary.
ü
Due to heat and
pressure these are transformed into metamorphic rocks.
ü
Fossils are not found
in the igneous rocks.
ü
What are fossils?
ü
Fossils are the
preserved remains or traces of animals, plants and other organisms from the
remote past.
ü
The igneous rocks are of two types.
o
Intrusive rocks
And
o
Extrusive rocks
Intrusive Rocks:
ü When the magma cools and becomes solid in the crust itself then
it is intrusive rocks.
ü The Granite and Dolomite
are the examples for intrusive igneous rocks.
Extrusive Rocks:
ü
If the
magma solidifies after extruding to the surface then it is called extrusive
rocks.
ü
These are
also known as volcanic rocks
ü
The Basalt rock
is an example for extrusive
rocks.
ü
(Note: The Deccan Plateaus are formed by
the Basalt rocks).
SEDIMENTARY ROCKS:
 |
| SEDIMENTARY ROCK |
ü The word sedimentary means settling.
ü Sometimes because of the external pressures
the rocks roll down hit each other and carried away to the different places and
are called sediments.
ü When these come together to form a big rock
it is called sedimentary rocks.
ü These are also called secondary rocks.
ü The sedimentary rocks are also called
stratified rocks as they are deposited in the distinct layers
ü The Sand Stone, Coal and Lime Stone are the example for sedimentary rocks.
ü The Himalayan foot hills are formed by the
sedimentary rocks.
ü The sedimentary rocks occupy 3/4th
of the earth’s surface.
ü The fossils are found in sedimentary rocks.
ü (As we discussed) they are formed form the
organic matter derived from the plant or animal remains.
ü The oil and petroleum is extracted from the
organic matter trapped between the layers of sedimentary rocks.
METAMORPHIC ROCKS:
 |
| METAMORPHIC ROCK |
ü Metamorphic means change of form.
ü Under great heat and pressure the igneous and sedimentary rocks
change to metamorphic rocks.
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