The Rock Cycle
The Earth…
It’s always changing…
Every Rock Tells a Story….
All rocks that we have on earth today are made up of all the same
stuff as the rocks that dinosaurs walked, crawled, or swam over.
While the stuff that rocks are made of has stayed the same, the
rocks themselves, have not.
Over time rocks are recycled into new rocks
QUESTIONS???
 What are some modern uses of rocks?
 How does a rock form?
When classifying a rock sample geologists
observe the rock’s color and texture and
determine its mineral composition. These
observations help identify what type of
rock it is.
•
Texture: the size, shape, and pattern of the rock’s grain.
•
Color: the apparent color of the rock, on the inside and
the outside.
•
Mineral composition: The minerals that make up the
different parts of a rock.
The Rock Cycle
Another look at the Rock Cycle
What are the 3 major
rock types and how can
they change from one
type to another type?
Rocks are classified by how
they formed and what they’re
made of. There are 3 general
classes of rocks:
•Igneous Rocks
•Metamorphic Rocks
•Sedimentary Rocks
Igneous Rocks
Igneous means “born of
Igneous Rocks
Igneous Rocks… are formed when lava
and magma crystallize to form solid
rock.

QUESTION???
How is lava different from
magma?
Magma vs. Lava
•
•
•
•
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All igneous rocks differ from one another in what they
are made of and how fast they cooled.
The longer it takes for the magma or lava to cool, the
more time mineral crystals have to grow. The more
time the crystals have to grow the coarser the texture
of the resulting igneous rock.
Magma is a hot liquid made of melted minerals. When
magma pours onto the earth’s surface it is called lava.
Igneous rock can form underground, where the
magma cools slowly. Or, igneous rock can form above
ground, where the magma cools quickly.
The crystals grow together and form one igneous rock.
Bedrock
Magma
Three Dike Hill
Big Bend National Park, Texas.
3 Ways a Rock Can Melt
Temperature – An increase in temperature
deep within the Earth’s crust can cause
the minerals in a rock to melt.
Pressure – The high pressure deep within
the Earth forces minerals melt from
intense heat and pressure.
Composition – Fluids like water and carbon
dioxide enter a rock that is close to its
melting point. When these fluids combine
with the rock, they can lower the melting
point of the rock enough for it to melt and
form magma.
2 Types of Igneous Rocks
•
•
INTRUSIVE IGNEOUS ROCKS – When
igneous rocks are formed by magma that
cools BENEATH Earth’s surface, they are
called intrusive igneous rocks
EXTUSIVE IGNEOUS ROCKS – When
igneous rocks are formed by LAVA ON
Earth’s surface, they are called extrusive
igneous rocks
INTRUSIVE IGNEOUS ROCK
Enchanted Rock, near Llano, TX is exposed
intrusive formation made of granite.
EXTRUSIVE IGNEOUS ROCK
Extrusive rock cools quickly on the surface and
contains either very small crystals or none at all.
Example of Igneous Rock
Lava flow
Fort Davis State Park, Texas
Into the Bedrock
On top (Exit)
Intrusive (has crystals) Extrusive (no crystals)
Sedimentary Rocks
Sedimentary Rocks…are formed when
sediments (sand clay, and silt) are
compressed and become solid rock

QUESTION???
Can you name the 4 ways
Sedimentary Rock can be
formed?
Formation of Sedimentary Rocks
•
Erosion
•
Deposition
•
Compaction
•
Cementation
Example of Sedimentary Rock
Each layer takes approximately
10,000 years to make.
Lithification
The process by which sediment
becomes sedimentary rock
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•
•
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1st step :
2nd step :
3rd step :
4th step :
Erosion
Deposition
Compaction
Cementation
Elephant Rock near Big Bend
National Park, Texas
Sedimentary Rocks : Erosion
Destructive forces are
constantly breaking up
and wearing away all
the rocks on Earth’s
surface
The forces include heat
and cold, rain, waves,
and grinding ice
Erosion occurs when
running water or wind
loosens and carry away
the fragments of rock.
Santa Elena Canyon
Big Bend National Park
Santa Elena Canyon Big Bend National Park
Sedimentary Rocks: Deposition
•
Deposition is the process by which
sediment settles out of the water or
wind carrying it.
•
Moving water or wind slows and
deposits the sediment.
•
Sediment may include shells, bones,
leaves, stems, and other remains of
living things.
•
After sediment has been deposited,
the processes of compaction and
cementation change the sediment
into sedimentary rock.
•
Remains of living things in the
sediment may slowly harden and
change into fossils trapped in the
rock.
Overlook at La Cuesta
Big Bend Ranch State Park
Alluvial Fan near Madera Canyon
Big Bend Ranch State Park
Sedimentary Rocks: Compaction
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New sediments fit together
loosely, but gradually, thick
layers of sediment build up
creating new layers.
•
These layers are heavy and
press down on the layers
beneath them.
•
Compaction is the process that
presses sediments together.
•
Weight of the layers compacts
the sediments, squeezing them
tightly together.
•
The layers often remain visible
in the sedimentary rock.
Rock Formation in Ernst Tinaja Canyon
Big Bend National Park
Sedimentary Rocks: Cementation
•
Cementation is the process in which dissolved minerals
crystallize and glue particles of sediment together.
•
While compaction is taking place, the minerals in the
rock slowly dissolve in the water.
•
The dissolved minerals seep into the spaces between
particles of sediment.
•
It takes millions of years for compaction and cementation
to transform loose sediments into solid sedimentary rock.
Sedimentary Transformations
Point A: Water or wind deposits sediments (Deposition)
Point B: The heavy sediments press down on the layers
beneath (Compaction)
Point C: Dissolved minerals flow between the particles
and cement them together (Cementation)
Metamorphic Rocks
Metamorphic Rocks…are formed when an
existing rock is partially melted,
squeezed, or both

QUESTION???
What rock type does
metamorphic rocks come
from?
Metamorphic rocks
are rocks that have
"morphed" into
another kind of
rock.
These rocks were
once igneous or
sedimentary rocks.
How do sedimentary and
igneous rocks change?
The rocks are under tons and tons of pressure,
which fosters heat build up, and this causes
them to change.
If you exam metamorphic rock samples closely,
you'll discover how flattened some of the grains
in the rock are.
REVIEW
•
Geologists classify rocks by
observing color, texture and mineral
composition.
•
There are 3 general classes of rocks:
Igneous, Sedimentary, and
Metamorphic.
Igneous Rocks
Igneous Rocks… are formed when lava
and magma crystallize to form solid
rock.
There are 2 forms of Igneous Rocks
• Intrusive
• Extrusive
Sedimentary Rocks
Sedimentary Rocks…are formed when
sediments (sand clay, and silt) are
compressed and become solid rock
Sedimentary Rocks can be formed in 4
ways:
•
•
•
•
Erosion
Deposition
Compaction
Cementation
Metamorphic Rocks
Metamorphic Rocks…are formed when
an existing rock is partially melted,
squeezed, or both
Metamorphic rocks are formed from
Igneous and Sedimentary rocks
under extreme:
• Heat
• Pressure
What type of Rock?
SEDIMENTARY!
What type of Rock?
METAMORPHIC!
What type of Rock?
IGNEOUS!
What is any trace,
mark, or remains of
an organism called?
Fossils
The remains or imprints of living things of the past
found in Sedimentary rocks.
Fossils provide information about life and
conditions in the past.
Fossils of Sea Creatures
•
Oceans
once
covered
the area
•
What part
of the
ocean
Fossils of Plants
•
Plant fossils
can tell us
about the
ancient
environment
Animal Fossils
Animal fossils can
tell us
•About past
environments
•What the
animal ate
•How they lived
How old must a fossil be?
Now
that’s
old!!
10,000
years
What kind of rock
are fossils usually
preserved in?
They study
Why do
them to
scientists
learn about
study fossils? extinct
plants and
animals.