ROCKS, ROCKS, AND
MORE ROCKS!
Chapters 5 and 6 (Glencoe Earth Science)
What is a rock?
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A rock is a hard substance made of one or more
minerals
There are 3 types of rocks:
 Igneous
 Sedimentary
 Metamorphic
What’s an Igneous Rock?
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Formed when magma crystallizes
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These rocks are associated with fiery lava flows
 Lava
is magma that flows on the Earth’s surface
Types of Igneous Rocks
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Extrusive
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Formed from lava on Earth’s surface that cools quickly
Known as volcanic rock
Fine-grained
Intrusive
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Formed inside the Earth
Magma rises up into pre-existing rocks and hardens
Coarse-grained
Called “Plutonic” rocks after Pluto, the god of the
Underworld
These rocks commonly produce landforms
Granite is most common
What About Igneous Rocks?
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Useful as building materials
It’s Sedimentary, Watson!
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What’s a sedimentary rock?
A
rock formed from sediments
 Sediments are pieces of material that have been
carried/deposited by wind, water, ice, gravity, or
chemical precipitation.
 Sedimentary rocks form when these pieces are
cemented together
How do Sedimentary Rocks Form?
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Weathering
 Processes
that break rock into smaller pieces
 Chemical-minerals
in rock are dissolved or chemically
changed
 Physical-minerals are unchanged; rock fragments break off
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Erosion
 Movement
 Caused
of materials from one location to another
by wind, moving water, gravity, glaciers (ice)
 Eroded materials almost always moved downhill
Sediments, Classified
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Clastic Rock
 Refers
to fragments of rock and minerals created by
weathering and erosion
 Clastic comes from the Greek word for “broken”
 Classified by particle size
Deposition
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Occurs when sediments are laid down on the ground
or sink to the bottom of a body of water
Largest particles settle first than smallest are last.
Burial
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Most sediments are deposited in basins
(depressions)
As more sediments are deposited, the layers on the
bottom are exposed to more heat and pressure.
Causes lithification
 Physical
and chemical processes that turn sediment into
sedimentary rock
Process of Lithification
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1-Compaction
 Weight
of sediments forces them closer together
 Water is squeezed out of mud
 Sand resists compaction because of grain-to-grain
contact
Process of Lithification
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2-Cementation
 Temperatures
increase
 Mineral growth cements sediments together into solid
rock
Features of Sedimentary Rock
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Horizontal layering (bedding)
 Graded
bedding: particle size becomes more
coarse/heavy toward bottom layers
 Cross-bedding: formed as inclined layers of sediment
move forward across a horizontal surface
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Fossils
 Evidence
of once-living organisms
 These are sedimentary rocks!
Types of Sedimentary Rock (3 Types)
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Clastic Rock
 Most
common; formed from deposits of loose sediments
Types of Sedimentary Rock
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Chemical Rocks
 Formed
when water evaporates leaving minerals
behind
 Ex: Stalactites (upper), stalagmites
 (lower)
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Organic Sedimentary Rocks
 Formed
from remains of a once-living thing
 Ex: limestone (Calcium Carbonate for seashells)
Why are Sedimentary Rocks
Important?
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It allows us a “snapshot” of surface conditions in
Earth’s past.
Energy Resources
 Coal,
Oil, Natural gas are found in sedimentary rock
 Many metals are mined from sedimentary rocks
 Used in making cement (limestone)
 Used in making blocks for walls (sandstone, limestone)
Metamorphic Rock
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When high temperature and pressure combine to
alter the texture, mineralogy, or chemical
composition of a rock without melting it.
Metamorphism = Change and form
This high pressure for a rock to become metamorphic
can happen in 2 ways:
Vertical Pressure caused by the
weight of overlying rock
Compressive forces generated as
rocks are deformed during
mountain building.
The Rock Cycle
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Continuous changing and remaking of rocks
Rocks are constantly being recycled from one type to another
Example of the Path of a Rock Through
the Rock Cycle
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Granite (igneous rock)
Wind/rain erodes exposed rock, bits flake off, carried
to bottom of stream  carried to river, along with
other sediments  carried to sea, deposited
Deposits build up  form sandstone (sedimentary
rock)
Sediments continue to be buried and are under more
pressure/higher temps  pressed together even more
 form quartzite (metamorphic rock)AND THE CYCLE
CONTINUES…