1. Petrology is the branch of geology that studies the formation, classification, and occurrence of rocks. 2. There are three main types of rocks: igneous, sedimentary, and metamorphic. Igneous rocks form from the cooling of magma or lava. Sedimentary rocks form through the compaction and cementation of sediments. Metamorphic rocks form through heat and pressure altering existing rocks. 3. Rocks are composed of minerals, which are naturally occurring inorganic solids with distinct physical properties used to identify them.

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PETROLOGY
The branch of Geology
dealing with various aspects
of rocks such as formation of
rocks, chemical and
mineralogical classification
occurrence of rocks, their
rocks

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INTRODUCTION
 In geology, rock or stone is a
naturally occurring solid
aggregate of one or more
minerals or mineraloids .
 A rock is an aggregate of
minerals. It may be up of one

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Classification of Rocks

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IGNEOUS ROCKS
EXTRUSIVE
 Volcanic- Fine-grained
INTRUSIVE
 Plutonic- Coarse-grained

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Igneous:
- Form when liquid rock cools and solidifies
Intrusive
 Cools below the earths surface
(slowwwwly!)
 Magma
 “Plutonic”
Extrusive
 Cools at the Earths
surface (quickly!)
 Lava
 “Volcanic”

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The longer the rock takes to cool, the larger
the crystals!
 Cools slow …..Large crystals
 Cools fast …….small crystals
 Cools immediately……NO Crystals (glass)

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Igneous rocks
1. The rocks that have formed from an originally hot
molten material through the process of cooling and
crystallization are called as igneous rocks .
2. Magma-The hot molten material occurring
naturally below the surface of the earth is called
magma . It is called lava when erupted through
volcanoes. Igneous Rocks are formed both from
magma and lava

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a) Volcanic Rocks-These are the igneous rocks formed
on the surface of the earth by cooling and
crystallization of lava erupted from volcanos. The
grain size of the crystals formed in these rocks are
very fine and microscopic.
b) Plutonic rocks-These are igneous rocks formed at
considerable depths generally between 7-10km below
the surface of the earth
c) Hypabyssal rocks-These igneous rocks are formed at
intermediate depths , generally up to 2 kms below the
surface of the earth.

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Engineering uses of igneous rocks
 Basalt and other dark colour igneous rocks are very
strong hence are used for foundations and road
stones etc
 Are also used for foundation of dams and reservoirs.

14. z SEDIMENTARY ROCK
 Sedimentary rock is formed by the deposition of
multiple layers of sediment in a process known as
lithification.
 Once deposited, the weight of new layers compacts
previous layers with such a force that they fuse
together.
 Over millions of years the layers continuously build up
before geological processes leave them exposed and
accessible for quarrying operations.

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Classifications of sedimentary rocks
 1.Clastic(fragmental)-made by
compaction and cementation of
fragments and are identified by
size of fragments.
 2.Non-clastic-non-clastic
sedimentary rocks form from
chemical reactions, chiefly in the
ocean.

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18. z Metamorphic
 Rocks that are changed due to extreme heat and/or
pressure.
 DO NOT MELT!!! (they recrystalize)
Metamorphic rocks become…
1. Harder
2. More dense
3. Banded or foliated
4. Distorted

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METAMORPHIC ROCK FORMATION
 1.Metamorphic rock form by
heat and pressure changing
one type of rock into another
type of rock.
 2.Metamorphic rocks form
near intrusions , at plate
subduction zones and in

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Identifying Characteristics of Rocks
Igneous
 Intergrown crystals
 Glassy texture
Sedimentary
 Cemented fragments
(sediments)
 Fossils
 Organic material
Metamorphic
•Banding
•Foliated

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 Minerals are the
ingredients of
rocks.
Or
 Rocks are made
up of minerals.

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Minerals
 Defn: naturally occurring,
inorganic elements or
compounds with specific physical
and chemical properties.

25. zMineral Properties
 Used to identify minerals
1. Color
 Least useful property in identifying
minerals.
 Why?

26. z All of these are varieties of quartz!

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2.Streak
 The color of a minerals powder.
 “streak test”

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3. Luster
 How the minerals surface reflects
light.
 Metallic vs. non- metallic.

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4. Hardness
 The ability of a mineral to resist being
scratched.
 “Scratch test”
 If mineral A can scratch mineral B, what
does that tell us about the relative
hardness of each mineral?

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Moh’s Hardness Scale
Soft
Hard

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5. Fracture/ Cleavage
Fracture
 Mineral breaks
unevenly or
irregularly
Cleavage
 The tendency of a
Mineral to break
evenly along its
weakest plane.

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34. z6.Crystal Form
 Some minerals tend to form crystals that
aid in the identification of the mineral.

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7.Specific Gravity
 The ratio of the density of the mineral to
the density of water (1 g/cm3)
 If a mineral has a specific gravity of 5 that
means it is 5 times as dense as water.

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8. Others
 Acid test – Calcite
 Magnetic – Magnetite
 Taste - Halite

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A minerals
properties are due to
the internal
arrangement of its
atoms.

38. Silicate Minerals
• Minerals that contain a combination of
silicon and oxygen.
Silicon-oxygen tetrahedron
The basic structural unit of silicate minerals

39. Weathering and Erosion
Essential Question: How does weathering and
erosion shape our Earth?

40. What is Weathering?
What are the two forms of weathering?
Define each.

41. What is Mechanical Weathering?
• Mechanical weathering is breaking down by natural or
physical processes
– Ice
– Animals
– Plant Growth

42. What is Chemical
Weathering?
• Chemical weathering occurs when minerals are
chemically changed causing them to dissolve or change to
another mineral
– Oxidation
– Acid
– Water

43. DISCUSS with your table:
• What is the connection between weathering and
erosion??
• Why did we learn weathering first??
• How does this affect the Earth? Us?

44. EROSION:
DESCRIPTION:
•The movement of rock
particles from a specific
location
Add to your notes!

45. EROSION
CAUSED BY:
WATER
WIND
ICE
GRAVITY
WAVES
Add to your notes!

46. 1. What is erosion?
2. What type of mass
movement is shown in
this illustration?
3. What are the 5 agents
of erosion?