Classifying rocks
Rocks are made up of two or more
minerals.
 About 20 minerals make up most of the
earth’s rocks.
 When studying rocks, geologists
observe the mineral composition, color
and texture of the rock.

This rock
contains
three
minerals.
Rock color
A rock’s color can indicate the rock’s
mineral composition. Certain minerals
are light in color while other minerals are
dark in color.
 Granites are usually light
 Basalts are usually dark

Rock Texture
 Texture
1)
2)
3)
involves 3
components:
Grain size
Grain shape
Grain pattern
Fine grained
Coarse grained
Rounded grains
Jagged grains
Nonbanded
banded
Three Groups of Rocks



Igneous – form from
the cooling of
magma or lava
Sedimentary – form
when particles of
rocks are pressed &
cemented together
Metamorphic –
when existing rocks
are changed by
heat, pressure, or
chemical reactions.
This is NOT the correct answer!
How do Igneous Rocks Form?
First rocks must melt into Lava/Magma!
Increase in Temperature – rocks melt
 Decrease in Pressure – hot rock can
remain solid if it is under high pressure
deep within the Earth. When hot rock
rises to the surface, the pressure goes
down and rocks can melt.
 Addition of Fluids – when fluids, such as
water, mix with rock, the melting
temperature of the rock decreases and
the rock can melt.

IGNEOUS ROCKS
Igneous rocks are
classified according to
their origin, texture,
and mineral
composition.
 ORIGIN:
Extrusive – formed from
lava that has erupted
(outside-”exit”).
Intrusive – formed when
magma hardens
under the earth’s
surface (inside).

Most common
Extrusive rock
Basalt
Most common
Intrusive rock
Granite
Types of Magma/Lava


Different compositions
of lava or magma
determine the types of
igneous rocks formed.
Magma that contains
sodium, potassium,
and aluminum will
form light colored
called Felsic rocks
such as granite.

If the magma is high
in iron, magnesium
and calcium will form
dark colored rocks
called Mafic such as
basalt.
Extrusive vs. Intrusive
 Extrusive



Rapid cooling
Small crystal size;
fine grained
Can have a glassy
texture
 Intrusive


Slow cooling
Larger crystals;
coarse grained
Uses of Igneous Rock

Igneous rock has
been used for
thousands of years
for buildings and
statues. Granite is
the most widely
used igneous rock.
Borax Experiment

Final Observations
 Trace two petri dish circles into your




notebook.
Inside one circle draw what you see with the
unaided eye.
Inside the second circle, draw what you see
with the magnifying glass.
Describe the process we used to create
these crystals.
How do these crystals compare with
igneous rock creation?
SEDIMENTARY ROCKS

Sediments are small bits & pieces of
rocks, shells, sand, bones, or parts of
plants.
This is
called silt
Can you see
the shells?
Sediments can be carried
away by water to be
deposited somewhere else.
From Sediment to
Rock
• Particles are
carried away
by wind or
water
• Particles are
deposited
• DEPOSITION
Erosion
Compaction
• Particles are
squeezed
together by
pressure
• Particles
are glued
together as
mineral
solutions
harden
Cementation
Sedimentary rock formation
Formation under water
The most noticeable feature of sedimentary rocks
are layers called strata. Stratification is the
process in which sedimentary rocks are arranged
in layers.
Three Major Types of
Sedimentary Rocks
Clastic
Organic
• Rock formed by rock fragments that are cemented together;
sometimes visible large fragments, sometimes small, fine
fragments
• Two common types are conglomerates, sandstone, breccias
• Rocks formed by the remains of plants/animals that are
cemented together.
• Two common types are coal and limestone
• Formed when minerals dissolved in water are
crystallized when the water evaporates away
Chemical • Calcite and Halite can form this way.
CLASTIC SEDIMENTARY ROCKS
This is a breccia.
Notice the jagged
edges.
These are conglomerates
This is sandstone.
The individual fragments
Are not easily seen.
This is shale, splits
easily into thin sheets.
ORGANIC SEDIMENTARY
ROCKS
Limestone – forms in the
ocean from shells, corals,
calcite skeletons being
compacted
Fossils are found mainly
In sedimentary rocks.
Coquina- a special type of limestone
In which shells can be easily seen
Coal is one of the most
important organic rocks.
The formation of COAL
Coal is made from once
living plants & animals.
Limestone is formed from corals,
and other sea animals.
These shells and
animal remains get
crushed and cemented
together over time to
form limestone.
Limestone formations
These are called
pancake rocks!
These are
located in
Vietnam.
More limestone formations
Here are some
hot springs in
limestone.
Many cave
formations are
made of
limestone.
Chemical Sedimentary Rocks
Gypsum and Halite are two of the most
common chemical sedimentary rocks.
 They can also be minerals!
 They formed by dissolved chemicals
crystallizing as water evaporates.
 For this reason they are sometimes
called EVAPORITES.

This is GYPSUM in a cave in
New Mexico. Gypsum is
Calcium Sulfate. It is used
In plaster of paris, drywall,
and Cement.
This is a chemical
form of
limestone. It is
called TUFA.
Coral Reefs are responsible for
much of the limestone on earth.

Coral is an animal much like a sea
anenome. They have tentacles and eat
plankton. To protect their soft bodies
they secrete a hard substance called
CALCITE. When they die, these calcite
shells remain.
Ancient Coral Reef vs.
Living Coral Reef
Sedimentary Rock Experiment
What are some similarities between
the three samples?
2. What are some of the differences?
3. Are the grain sizes in the samples
the same?
4. How would you describe the shapes
of the grains you observe?
1.
Sedimentary Rock Experiment
Closure
1. Draw a cycle, cartoon or some
animation of your understanding of the
formation of sedimentary rocks. Color
your drawing if time permits.
2. Draw and label the layering of the
sediments after they settle.
METAMORPHIC ROCKS
Heat (temps between 150-1000 degrees
celcuis) & pressure deep in the earth can
change any rock into a metamorphic rock.
They can form from igneous, sedimentary and
other metamorphic rocks.
 Extremely high temps and pressures deep in
the earth can actually change a rocks mineral
composition.

Stories in Stone - Metamorphic
1.
2.
3.
Form 20 red and 20 blue small
marble sized spheres.
Form the yellow clay into a
pancake about the size of your
hand.
Break the green in half and form
2 pancakes.
Metamorphic Rock Experiment
1.
2.
3.
4.
5.
6.
Observe and describe the layering in the
piece of the model you just cut off.
How was your fist similar to what happens
when metamorphic rock is formed?
How was your fist different?
How is the piece of the model you
“metamorphized” different from the piece
you cut of that wasn’t “metamorphized”?
Describe the metamorphic layers.
How do metamorphic rocks differ from
igneous or sedimentary rocks?
Two Types (textures) of
Metamorphic Rocks
FOLIATED
NONFOLIATED
Rocks grains are
arranged in parallel
bands or layers
Common examples:
Slate, gneiss, schist
Grains are arranged
randomly.
Common examples:
Marble, quartzite
Non-foliated Metamorphic Rocks
With pressure, granite becomes gneiss
(foliated rock). Igneous rock is changed
to a metamorphic rock.
Increasing pressure causes greater
foliation
Increasing Pressure
SHALE
SLATE
SCHIST
GNEISS
Index Minerals
Some minerals, such as quartz, can form
at many different temperatures.
 Other minerals, such as garnet, form only
at certain temperatures and pressures.
 Therefore, rocks that contain minerals like
garnet probably also formed at those
temperatures and pressures and are
called index minerals.
 Index minerals and can indicate the
temperature and pressure or depth at
which a rock formed.

Two ways rock can go through
Metamorphism

Regional metamorphism –
high pressures and
temperatures cause the
rock in a large area to
change. It can happen
where rock is buried deep
below the surface or at
convergent boundaries.
Two ways rock can go through
Metamorphism
1.
Contact metamorphism – rock is heated
by nearby magma. The nearer the rock
is to the magma, the more changes
occur.
USES OF METAMORPHIC ROCK
World’s Largest Marble Quarry
Tate, GA
Uses of SLATE
Rock Cycle Simulation
1.
2.
3.
4.
5.
Where did you spend the most time?
Why is the rock cycle called a cycle?
Why did everyone not follow the
same path?
How does a rock become Igneous?
Sedimentary? Metamorphic?
Where are rocks being born and
transformed today?
Rock Cycle Simulation
5.
6.
7.
8.
Where are rocks being born and
transformed today?
How much of the rock cycle can be
observed? How much must be inferred?
How are people affected by movement
of Earth material through the rock
cycle?
If each step of our rock cycle game was
200,000 years, what was the time
period represented in the game?
The Rock Cycle
It is a series of processes
in the earth’s crust, mantle
and on the earth’s surface
that SLOWLY change
rocks from one kind to
another.
Click on the link for a Rock
Cycle animation