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



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.


v  Parent rocks.


v  Volcanic rocks.


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


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).



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.



ü  Metamorphic means change of form.

ü  Under great heat and pressure the igneous and sedimentary rocks change to metamorphic rocks.

ü  Examples:

v  Coal changes into Graphite

v  Lime stone changes into Marble

v  Clay change into slate

v  Granite changes into Gnesis