Rocks of the Earth

1. Chapter 09
Rocks of the Earth

2. 1 Samuel 2:2
There is no one holy like the
LORD, Indeed, there is no one
besides You, Nor is there any
rock like our God.

3. What Are Rocks?
•
Rocks are solid materials of the Earth’s crust
•
They are made of substances known as minerals and are formed in
various ways
•
Landforms such as mountains and volcanoes are made up entirely of
rocks
•
Geologists classify rocks into three types:
 Igneous
 Sedimentary
 Metamorphic

4. Igneous Rocks
•
•
Igneous rocks are molten material
(called magma) that has cooled
and solidified
The texture of rock is affected by the
speed at which magma cools
and hardens:
Coarse-grained igneous
rocks are formed when
magma cools and
hardens inside the Earth
Lava
 If magma cools and hardens slowly, a
coarse-grained rock results e.g. granite
 If magma cools and hardens quickly, a
fine-grained rock results e.g. basalt
Fine-grained igneous rocks
are formed when the lava
cools and hardens on the
Earth’s surface
Magma

5. Sedimentary Rocks
• Formation of sedimentary rocks
 Weathering and erosion break down or wear
down rocks into smaller pieces
 These tiny pieces of rock, together with
sand, clay and silt are called sediments
 Sediments are eventually deposited into rivers
and seas and form layers on river or sea beds
 As the layers of sediments pile up, weight of
the upper layers presses down the lower
layers, causing the sediments to cement
together and harden
 These solid, hardened layers of sediment are
called sedimentary rock
The weight of top layers
causes layers below to
cement and harden to
form sedimentary rocks

6. Sedimentary Rocks
• Texture of sedimentary rocks
depends on the size
of the original sediment
 If the size of the sediments is small,
sedimentary rocks
formed will be fine-grained
Shale
e.g. shale
 If the size of the sediments is big,
the rock will be coarse-grained
e.g. conglomerate
conglomerate

7. Sedimentary Rocks
• Some sedimentary rocks are
formed from the remains of
animals and plants e.g.
limestone
• The main characteristic of
sedimentary rocks is that they
are formed in layers which vary
in thickness and appearance
A limestone cave

8. Metamorphic Rocks
•
•
•
Metamorphic rocks are formed as a
result of intense pressure and heat
acting on igneous and sedimentary
rocks
This occurs due to crustal movements
or when the rock comes into contact
with molten magma
Pressure and heat sometimes cause
metamorphic rocks to have a foliated
appearance (bands)
e.g. slate
Slate

9. The Rock Cycle - continual process of change
in the rock types
2. Weathering and erosion
of rocks result in sediments
1. Igneous rocks are formed
from magma
Igneous
Rocks
Sediments
Magma
5. Metamorphic rocks
that are buried deep
in the Earth melt in
the mantle
Metamorphic
Rocks
3. Large and small
sediments pile up
in layers, and are
cemented and
hardened to form
sedimentary rocks
4. Under intense heat and
pressure, sedimentary
and igneous rocks change
into metamorphic rocks
Sedimentary
Rocks