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streak the
EQ: How are rocks
formed?
Standard S6E5.c
Classify rocks by their
process of formation.
EQ: How Are Rocks Classified?
• What three characteristics
do scientists use to identify
rocks?
• What are the three groups
into which geologists
classify rocks?
• What is a rock’s texture?
• What do the three major
groups of rock have in
common? How are they
different?
How geologists Classify Rocks
• Rocks are made of minerals and a mixture
of other materials
• Some rocks are made of a single mineral
• When studying a rock sample, geologists
observe the rock’s texture, origin and
mineral composition
A Rock’s Texture
• A rock’s texture is the size, shape, and pattern of
the rock’s grains
Grain Size
a. fine-grained (small-basalt)
b. coarse-grained (large-granite)
Grain Shape
a. smooth and rounded (conglomerate)
b. jagged (breccia)
Grain Pattern
a. foliated (gneiss)
-lie in flat layers
-wavy, swirling patterns
b. nonfoliated (marble)
c. looks like rows of multicolored beads
d. occur randomly
No Visible Grain
a. have no apparent grains
. vy,
Mineral Composition
• By looking at a small sliver of a rock under a
microscope, geologists can observe the size and
shape of the crystals and identify the minerals
the rock contains
• Also, geologists can do tests to identify the
physical properties of the minerals inside the
rock.
•
•
mafic= dark-colored rocks (poor in silica) (basalt)
felsic = light-colored rocks (rich in silica) (granite)
Rock Origin
Origin how and where the rock was formed
1. igneous rock = forms from the melting, cooling and hardening of
molten rock
a. extrusive= formed above the surface (lava)
b. intrusive = formed below the surface (magma)
2. sedimentary rock = forms in layers from other
rocks, plants, and animals through a
process of weathering,
erosion, deposition, compaction and cementation
a. clastic rock
b. organic rock
c. chemical rock
3. metamorphic rock = formed when existing
rock is changed by heat, pressure, or chemical reactions
a. foliated rock
b. nonfoliated rock
Compare and Contrast Rocks
Compare – Rocks in each group make up
the Earth’s crust and are composed of
minerals and other materials
Contrast – Rocks are different in the way
they are formed
How do igneous rocks form?
• What characteristics are
used to classify igneous
rocks?
• Describe three (3) ways
in which igneous rocks
differ.
• What is the difference
between extrusive and
intrusive rocks? Give an
example of each.
• Why are some igneous
rocks dark and others
light?
Origins of Igneous Rock
• Igneous rocks are classified by their origin.
• Igneous rocks are classified by the texture of the grains
• Igneous rocks are classified by the mineral composition
of the rock
• Igneous rock forms when magma cools and hardens.
• Three ways magma can form:
– heat/rise in temperature
– pressure released
– rock changes composition
Composition and Texture of Igneous
Rock
• Igneous rocks differ from one another in what
they are made of, how fast they are cooled and
where the rocks form.
• Composition –
• Igneous rock that is rich in silicon and lightcolored are called felsic rock.
• Igneous rock that is poor in silicon and darkcolored are called mafic rock.
• Texture –
– Fine-grained (small) = cools quickly
– Coarse-grained (large) =cools slowly
Origin of Formation
• Igneous rock formations are located below and
above Earth’s surface.
• Intrusive igneous rock – Intrusive rock (granite) forms
when magma hardens (beneath) Earth’s surface.
– coarse-grained (large grains)
– below Earth’s surface
– ex. granite
• Extrusive igneous rock – Extrusive rock (basalt)
forms from lava that has erupted (onto) Earth’s surface.
– fine-grained (small grains)
– on the Earth's surface
– ex. basalt
How do igneous rocks form?
• Igneous rocks are classified according to their origin, texture,
and mineral composition.
• Igneous rocks form either from lava, above the earth’s surface
or magma, below the earth’s surface.
• They also differ in texture according to the size and shape of
their mineral grains. (course-grained or fine-grained)
• Igneous rocks differ in mineral composition depending on how
much silica and other minerals are present. (felsic or mafic)
• Dark igneous rocks form from magma or lava low in silica
content (mafic).
• Light igneous rocks form from magma high in silica content
(felsic).
• Light-colored rocks are less dense than the dark-colored
rocks.
Uses of Igneous Rock
• Most igneous rocks are hard, dense, and
durable.
• Ancient Native Americans used obsidian for
making very sharp tools for cutting and scraping.
• Granite is used as a building material such as
decorative stonework, curbstones, and floors..
• Basalt is crushed to make gravel.
• The rough surface of pumice makes a good
abrasive for cleaning and polishing.
• Perlite is often mixed with soil for starting
vegetable seeds.
Quick Check
1. Which of the following are ways magma is
formed?
a.
b.
c.
d.
by compaction and cooling
by melting and cooling
by changes in composition
by weathering and erosion
Quick Check
2. What kind of texture does igneous rock
have when magma cools slowly?
a.
b.
c.
d.
coarse-grained
large-grained
fine-grained
medium-grained
Quick Check
3. What kind of texture does igneous rock
have when magma cools rapidly?
a.
b.
c.
d.
coarse-grained
medium-grained
large-grained
fine-grained
Quick Check
4. What kind of rock is formed when magma
intrudes into other rock?
a.
b.
c.
d.
extrusive igneous rock
sedimentary rock
intrusive igneous rock
organic sedimentary rock
Quick Check
5. What kind of rock is formed from lava that
cools on Earth’s surface?
a. organic sedimentary rock
b. sedimentary rock
c. intrusive igneous rock
d. extrusive igneous rock
How is sedimentary rock formed?
• Describe the origin of
sedimentary rock.
• Describe the three
main categories of
sedimentary rock.
• Describe three types
of sedimentary
structures.
What is sedimentary rock?
• Sedimentary rocks
form from particles
deposited by water
and wind.
• After sediment has
been deposited, the
processes of
compaction and
cementation change
the sediment into
sedimentary rock.
Forming of Sedimentary Rock
• Weathering- the breaking down of rock
• Erosion – occurs when running water or wind
loosen and carries away fragments of rock.
• Deposition- the process in which sediment
settles out of the water or wind carrying it.
• Compaction- the process that presses sediment
together.
• Cementation- the process in which minerals
crystallize and glue particles of sediment
together.
Types of Sedimentary Rock
• Geologists classify
sedimentary rocks
according to the type of
sediments that make up
the rock.
• There are three major
groups of sedimentary
rocks: clastic rocks,
organic rocks, and
chemical rocks.
Clastic Rocks
• A clastic rock is a
sedimentary rock that
forms when rock particles
are squeezed together.
• Examples of clastic rocks:
–
–
–
–
Shale
Sandstone
Conglomerate
Breccia
Clastic Rock: Shale
• Shale forms from tiny
particles of clay.
• Shale feels smooth,
and splits easily into
flat pieces
Clastic Rock: Sandstone
•
Sandstone forms
from the sand on
beaches, on the
ocean floor, in
riverbeds, and in sand
dunes.
• Sandstone is formed
when small particles
of sand are pressed
and cemented
together.
•
.
Clastic Rock: Conglomerate and Breccia
• Conglomerate is a
rock made up of large
particles with rounded
edges.
• Breccia is a rock
made up of large
fragments with sharp
edges.
Organic Rocks
• Organic rock forms from
the remains of plants and
animals and are deposit
in thick layers.
• The term “organic” refers
to substances that were
once part of living things.
• Three important organic
rocks:
– Coal
– Limestone
– Chalk
Organic Rock: Coal
• Coal forms from the
remains of swamp
plants buried in water.
• Over millions of
years, they slowly
change into coal.
Organic Rock: Limestone
• The hard shell of living
things produces
limestone.
• Chalk forms from
sediments made of
skeletons of
microscopic living things
found in the ocean.
Chemical Rocks
• Chemical rock forms
when minerals that are
dissolved in a solution
crystallize.
• Chemical rocks can also
form when mineral
deposits left when seas
or lakes evaporate.
• Examples:
– Rock salt
– gypsum
Sedimentary Rock Structures
• The most important feature of sedimentary rock is
stratification.
• Stratification is the process in which sedimentary rocks
are arranged in layers.
• Strata differ from one another depending on the kind,
size, and color of their sediment.
• Ripple marks (1) are made by the motion of wind and
water waves on lakes, oceans, rivers, and sand dunes.
• Mud cracks (2) form when fine-grained sediments at the
bottom of a shallow body of water are exposed to air and
dry out.
• Rain-drop (3) impressions can be preserved in finegrained sediments, as small pits with raised rims.
Uses of Sedimentary Rocks
• Sandstone and limestone are used as
building materials.
• The White House in Washington, D.C. is
built of sandstone.
• Limestone is also used to make cement.
Quick Check
1. Which process forms sediment?
a.
b.
c.
d.
weathering
cementation
compaction
deposition
Quick Check
2. What are strata?
a.
b.
c.
d.
mineral fragments
minerals crystallized out of solution
layers in sedimentary rock
fossils in sedimentary rock
Quick Check: Sedimentary Rock
3. What kind of sedimentary rock is
made of fragments of rocks
cemented together by a mineral?
a.
b.
c.
d.
organic
stratified
chemical
clastic
Quick Check
4. What kind of sedimentary rock is
made from solutions of dissolved
minerals in water?
a.
b.
c.
d.
organic
chemical
stratified
clastic
Quick Check
5. What kind of sedimentary rock is
made from fossils?
a.
b.
c.
d.
organic
stratified
chemical
clastic
Quick Check
6. What is the process called in which
sedimentary rocks are arranged in
layers?
a.
b.
c.
d.
erosion
extrusion
weathering
stratification
How is metamorphic rock formed?
• How are metamorphic
rocks formed?
• Describe two ways a
rock can undergo
metamorphism.
• Describe the
difference between
foliated and
nonfoliated
metamorphic rock.
How Do Metamorphic Rocks Form?
• Metamorphic rock is formed when existing
rock is changed by heat, pressure, or
chemical reactions.
• Heat and pressure deep beneath
Earth’s surface can change any rock
into metamorphic rock.
• Metamorphic rocks are classified by the
arrangement of their mineral grains.
Textures of Metamorphic Rock
• The two types of metamorphic rocks are
called foliated rock and non-foliated rock.
• Foliated rock is when the grains are
parallel or arranged in planes or bands.
– gneiss (from granite)
– Slate (from shale)
• Non-foliated rock refers to where the
grains are arranged randomly.
– Marble (from limestone)
– Quartzite (from sandstone)
Foliated Metamorphic Rock
»
»
»
• Schist
Gneiss
Nonfoliated Metamorphic Rocks
Quartzite
Marble
Composition of Metamorphic Rock
• Metamorphism occurs when temperature and
pressure inside the Earth’s crust change.
• Minerals that were present in the rock when it
formed may not be stable in the new
temperature and pressure conditions.
• The original minerals change into minerals that
are more stable in these new environment.
• Some metamorphic minerals form only at certain
temperatures and pressures.
• Common metamorphic rock: slate, schist,
marble, and gneiss.
Metamorphic Rocks
• The texture or mineral composition of a rock can change
when its surroundings change.
• If the temperature or pressure of the new environment is
different from the one in which the rock formed, the rock
will undergo metamorphism.
• Two ways that rock can undergo metamorphism are by
contact metamorphism and regional metamorphism.
• Contact metamorphism happens near bodies of magma.
• Regional metamorphism occurs within Earth’s crust
when pressure builds up in rock very deep below other
rock formations
Metamorphic Rock Structures
• Metamorphic rock has features that tell
you about its history.
• In metamorphic rocks, these features are
caused by deformation.
• Deformation is a change in the shape of a
rock caused by a force placed on it.
• These forces may cause a rock to be
squeezed or stretched.
• Folds or bends in metamorphic rock are
structures that indicate that a rock has
been deformed.
Uses of Metamorphic Rock
• Marble and slate are the two most useful
metamorphic rocks.
• Marble can be cut into thin slabs and
easily polished (Taj Mahal).
• Slate , because it is foliated, splits easily
into flat pieces.
• Slate is used for flooring, roofing, outdoor
walkways, or chalkboards.
• Marble and Slate both come in a variety of
colors.
Summary…
• There are 3 major rock groups: igneous rocks
sedimentary rocks and metamorphic rocks.
• Igneous rocks form when molten rock cools and
hardens from magma or lava.
• Sedimentary rocks form from particles deposited,
pressed, and cemented together by water and wind.
• Metamorphic rocks form from heat and pressure, or a
chemical reaction.
• Forces inside Earth and at the surface produce a rock
cycle that builds, destroys, and changes the rocks in
the crust.
Quick Check
1. How does metamorphic rock form?
a. by intense heat and pressure
b. erosion, deposition, compaction,
cementation
c. melting into lava or magma, then
cooling into a new rock
d. by pressing together and then
cementation
Quick Check
2. Molten rock beneath Earth’s surface is
called
a.
b.
c.
d.
lava.
magma.
sedimentary rock.
igneous rock.
Quick Check
3. If you wanted to duplicate conditions in a
laboratory that produced metamorphic rock from
sedimentary rock, what would you need to do?
a. apply pressure to the rock
b. apply high temperature to the rock
c. apply high pressure and high temperature to the
rock
d. let the rock stand under water for a long time
Quick Check
4. Which of the following is a metamorphic
rock?
a.
b.
c.
d.
granite
sandstone
limestone
marble
Quick Check
5. Metamorphic rocks can be formed from
a. igneous rocks.
b. sedimentary rocks.
c. metamorphic rocks.
d. all rock groups.
Quick Check
6. The rock formed when granite changes to
a metamorphic rock is
a. marble.
b. basalt.
c. gneiss.
d. pumice.
Quick Check
7. Metamorphic rocks that have their grains
arranged in parallel bands or layered are
said to be
a. jagged grained.
b. foliated.
c. nonfoliated.
d. coarse grained.
Quick Check
8. The heat that changes a rock into
metamorphic rock comes from
a. friction of plate movement.
b. the sun.
c. the heat of the mantle.
d. chemical rocks in the crust.
Quick Check
9. Geologist classify metamorphic rock
according to
• A. the exterior color of the rock.
• B. the overall shape of the rock.
• C. the arrangement of the grains that
make up the rock.
• D. the degree of hardness of the rock.
Quick Check
10. Which type of rock is MOST LIKELY to
form layers?
•
•
•
•
A.
B.
C.
D.
Sedimentary
Igneous
Metamorphic
magma
Quick Check
11. The _________ of a rock is determined
by the sizes, shapes, and positions of the
minerals the rock contains.
12. ________ metamorphic rock contains
minerals that are arranged in plains or
bands.
13. The most characteristic property of
sedimentary rock is __________.
Quick Check
14. Sedimentary rock is classified into all of
the following main categories except
_________.
a. clastic sedimentary rock
b. chemical sedimentary rock
c. nonfoliated sedimentary rock
d. organic sedimentary rock
Quick Check
15. An igneous rock that cools very slowly
has a __________ texture.
a. foliated
b. fine-grained
c. nonfoliated
d. coarse-grained
Quick Check
16. Igneous rocks form when
a. minerals crystallize from a solution.
b. sand grains are cemented together.
c. magma cools and solidifies.
d. mineral grains in a rock recrystallize.
Quick Check
17. A __________ is a common structure
found in metamorphic rock.
a. ripple mark
b. fold
c. sill
d. layer
Quick Check
18. The process in which sediment is
removed from its source and transported
is called ____________.
a. deposition.
b. erosion.
c. weathering.
d. uplift.
Quick Check
19. Mafic rocks are
a. light-colored rocks rich in calcium, iron, and
magnesium.
b. dark-colored rocks rich in aluminum,
potassium, silica, and sodium.
c. light-colored rocks rich in aluminum,
potassium, silica, and sodium.
d. dark-colored rocks rich in calcium, iron, and
magnesium.
EQ: What is the rock cycle?
• What materials are
rocks made of?
• Describe four
processes that
change rock from
one type to another.
• What are the three
main classes of rock?
• Describe two
characteristics of
rock that are used to
help classify it?
What materials are rocks made of?
• Rock is describe as a naturally occurring
solid mixture of one or more minerals and
organic matter.
• Rocks are made of mixtures of minerals
and other materials, although some rocks
may contain only a single mineral.
• When studying a rock sample, geologists
observe the rock’s origin, color and texture
and determine its mineral composition.
What materials are rocks made of?
• Texture is described with terms based on grain size,
grain shape, and grain pattern.
• Most rocks are made up of tiny particles of minerals
or other rocks, which are called grains.
• A rock’s grains give it its texture.
• There are three major groups of rocks: igneous rock,
sedimentary rock, and metamorphic rock.
• These terms refer to how the rocks in each group
were formed (origin).
The Rock Cycle
• The rock cycle is a series
of processes in which a
rock forms, changes from
one type to another, is
destroyed, and forms
again by geological
processes.
• Rocks have been used by
humans to make tools
and weapons and to
construct buildings.
Processes That Shape the Earth
• Certain geological processes make and
destroy rock.
• These processes shape the features of the
Earth.
• Theses processes also influence the type
of rock that is found in a certain area of
Earth’s surface.
Processes That Shape the Earth
• Weathering is the process by which water,
wind, ice, and heat break down rock.
• Erosion is the process by which sediment
is removed from its source.
• Deposition is the process by which
sediment moved by erosion is laid down.
• Uplift is the process by which rock within
the Earth moves to Earth’s surface.
Illustrating the Rock Cycle
• Igneous rock is formed when magma or
lava is cooled and hardens and solidifies.
• Sedimentary rock is formed by the process
of weathering, erosion, deposition and
compaction and cementation.
• Metamorphic rock is formed by heat,
pressure or chemical change beneath
Earth’s surface.
Rock Classification
• Scientists classify rocks in detail by using
two important criteria – composition and
texture.
• Composition is the chemical makeup of a
rock; describes either the minerals or other
materials in the rock.
• Texture is the quality of a rock based on
the sizes, shapes, and positions of the
rocks grains.
Quick Check
1. Which of the following rocks is not
normally used as a construction
material?
a.
b.
c.
d.
marble
halite
limestone
granite
Quick Check
2. The process in which wind, water, ice,
and heat break down rock is called
a.
b.
c.
d.
uplift.
intrusion.
recystallization.
weathering.
Quick Check
3. What forms when rock partially or
completely melts?
a.
b.
c.
d.
limestone
reefs
ripple marks
magma
Quick Check
4. Scientists classify rocks
a.
b.
c.
d.
by composition and texture.
by volume.
by mass.
by color and size.
Quick Check
Solid mixture of one or more minerals and
organic matter:
a. composition
b. rock
c. erosion
d. texture
e. rock cycle
f. deposition
Quick Check
Process by which new rock forms from old
rock:
a. composition
b. rock
c. erosion
d. texture
e. rock cycle
f. deposition
Quick Check
Process by which sediment is removed from
its source:
a. composition
b. rock
c. erosion
d. texture
e. rock cycle
f. depositi
Quick Check
Process by which sediment is dropped and
comes to rest:
a. composition
b. rock
c. erosion
d. texture
e. rock cycle
f. depositi
Quick Check
The chemical makeup of a rock:
a. composition
b. rock
c. erosion
d. texture
e. rock cycle
f. deposition
Quick Check
Size, shape, and position of grains that
make up a rock:
a. composition
b. rock
c. erosion
d. texture
e. rock cycle
f. deposition