Rocks and its types

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