The document discusses the three main categories of rocks: igneous, sedimentary, and metamorphic. It provides details on the formation of different types of rocks within each category. Igneous rocks form from cooling magma, either underground or from volcanic eruptions. Sedimentary rocks form from the compaction and cementation of sediments. Metamorphic rocks form from changes to existing rocks through heat or pressure. Examples are given for common rock types within each category, along with brief descriptions of their formation processes.

1. Submitted by – Ravi Sah
Class – B.Ed. 4th semester
Roll no. – 36
NERIE-NCERT, Umiam, Meghalaya

2.  Rocks are made from minerals.
 A mineral is a naturally occurring
inorganic substance with a definite
chemical composition found on Earth.
 A rock may be composed of only one kind
of mineral such as pure limestone, which
is composed of calcite.
 Others may have more than one mineral
like granite which has three minerals –
quartz, feldspar and mica.

3.  There are 3 major categories of rocks –
1. Igneous
2. Sedimentary
3. Metamorphic

4.  Igneous rocks are formed from magma
that has cooled and hardened either
beneath the surface or from a volcanic
eruption.
 Coarse-grained rocks(rough) are from
magma.
 Fine-grained rocks(smooth) are from lava.
 Igneous rocks can be of different types
depending on how the magma cools.

5.  GRANITE – It is formed when magma cools
slowly under the surface of the Earth.

6.  BASALT – It is formed when volcanic lava
cools very fast and hardens quickly above
the surface of the Earth.

7.  OBSIDIAN – It is a dark-coloured igneous
rock that is formed when magma cools
quickly.

8.  PUMICE – It is a light-coloured igneous
rock that forms when frothy lava cools
quickly on the Earth’s surface.

9.  Sedimentary rocks are formed from layers
of sediments, created by weathering, and
erosion, that are laid down in horizontal
strata by water or wind and are squeezed
and stuck together.
 Fossils are usually found in sedimentary
rocks.

10.  SANDSTONE – It is formed when grains of
sand get compressed and cemented
together.

11.  LIMESTONE – It mainly consists of a
mineral called calcite which is formed
from the shells and skeletons of tiny sea
animals.

12.  SHALE – It is formed when layers of clay
and silt harden.

13.  CONGLOMERATES – It is formed when the
lower layers of sediments consist of
pebbles and sand.

14.  Metamorphic rocks are formed when
extreme pressure or heat is applied to
sedimentary or igneous rocks.
 The crystalline shape presses together
and changes their appearance which
makes them tougher and harder.

15.  MARBLE – It is formed when limestone
undergoes changes.

16.  QUARTZITE – It is formed from standstone.
It is hard and tough.

17.  SLATE – It is formed from shale. It splits
easily into thin sheets.

18.  GNEISS – It is formed from granite. It is
coarse grained and has irregular bands of
different colours.

19. ROCKS
 https://youtu.be/t0AS5G5v9co
REFERENCES
 https://www.slideshare.net/goatkell/rocks-
minerals-15180147
 https://www.slideshare.net/espinorachel/ro
cks-and-minerals-57767998
 https://www.slideshare.net/belalelnagar3/m
inerals-and-rocks-for-presentations
 https://www.slideshare.net/luchislinda/rock
s-and-minerals-55995096