Chapter 4- Rocks
Earth Science
Bell Work Lesson 4.1
• Rock- Natural, solid mixture of minerals/grains
• Grain- What mineralogists call the fragments that
make up a rock
• Texture- The grain size and the way the grains fit
together
• Magma- Molten or liquid rock underground
• Lava- Molten rock that erupts on Earth’s surface
• Sediment- Rock material that forms where rocks
are broken down into smaller pieces or dissolved
in water as rocks erode
• Rock cycle- The series of processes that change
one type of rock into another type of rock
Rocks
• A natural, solid
mixture of minerals or
grains
– Grain= fragments that
make up rock
• Mineral crystals, broken
bits of minerals or rock
fragments
• Can contain remains
of organisms or
volcanic glass
How to classify rocks?
• Two important observations:
– Texture
– Composition
Texture
• The grain size and the way the grains
for together
– Look at the size of the minerals or
grains
– Look at the arrangement of the minerals
or grains
– What is the overall feel of the rock?
Composition
• Classified by the minerals or grains
present in a rock
– Can tell a geologist where the rock
formed
• Certain minerals can suggest rock formed
under extreme temperature or pressure
Three major rock types
• Based on how
they form
– Can determine
where they formed
based on the
characteristics
• Three types:
– Igneous
– Sedimentary
– Metamorphic
Igneous rock
• When magma or lava
cools and crystallizes, it
creates this kind of rock.
– Magma= molten or liquid
rock underground
– Lava= molten rock that
erupts on Earth’s surface
• The crystals that grow
form the grains of the rock
• Can form in different
environments:
– Subduction zones, midocean ridges, hot spots (lots
of volcanoes)
Igneous rock cont’d
Sedimentary rock
• Sediment: rock
material that forms
where rocks are
broken down into
smaller pieces or
dissolved in water as
rocks erode
• Sediment, mineral
crystals, remains or
plants and animals
are building blocks of
sedimentary rock
Sedimentary rock cont’d
• Rock forms where
sediment is deposited
(added to a landform)
– Examples of where
sediment is deposited:
Rivers/streams, deserts,
valleys
• Loose sediment will
someday turn into rock
– Examples of where
sedimentary rocks can be
found: mountain valleys,
along river banks, beach
etc.
Metamorphic rock
• Rocks that are exposed to
extreme temperature and
pressure can change to
metamorphic rock
– Can happen along plate boundaries
– Can also happen if rock is exposed
to some chemical fluids
• Minerals change AND texture
changes when the rock changes
into metamorphic rock.
– Grains can look bent or twisted
Metamorphic rock cont’d
• Can form from ANY
rock (including other
metamorphic rock)
– Limestone (sedimentary
rock) metamorphoses
into marble
– Granite (igneous rock)
metamorphoses into
gneiss.
Rock Cycle
• The series of processes that
change one type of rock into
another type of rock
– Rocks are changing all the
time
• Slowly
• Because of forces within Earth
and on Earth’s surface
– Example: 1- Lava forms
igneous rock; 2- the rock is
exposed to Earth’s surface and
is eroded by water to form
sediment; 3- the sediment
cements together to form
sedimentary rock.
Rock cycle cont’d
• Some processes can only occur under
Earth’s surface
– Extreme pressure and temperature (and
melting)
• Some rocks that are made under Earth’s
surface change when uplifted to Earth’s
surface
– What changes can happen once on surface?
• Weathering, erosion, deposition, compaction,
cementation.
HOMEWORK Ch4 L.1
• Vocabulary words on flash cards
– MEMORIZE THEM FOR QUIZ
• Outline Lesson 1
• Lesson Review questions
– P. 116 #1-8
• QUIZ!!!!
LaunchLab p.111
• Obtain a rock sample
• Examine the rock with/without a
magnifying glass
• Describe rock in detail
–
–
–
–
Color
Texture
Anything weird/cool in it?
Any minerals/grains you can see?
• WRITE YOUR NAME ON PAPER AND
TURN IT IN
Ch4 L.2 Igneous Rocks
Bell Work Ch4 L.2
• Extrusive rock: When volcanic material
erupts and cools and crystallizes on
Earth’s surface
• Volcanic Glass: Rock that forms when
lava cools too quickly to form crystals
• Intrusive Rock: Igneous rocks that form as
magma cools slowly underground
Essential questions:
• How do igneous rocks form?
• What are the common types of
igneous rocks?
Launch Lab p.119
• Observe what happens when I drop hot,
melted sugar into your beaker of water.
– One time slowly
– One time quickly
• Record what happens
– What is the difference between the two?
• WRITE YOUR FULL NAMES ON IT AND
TURN IT IN.
• WORK IN PAIRS.
Igneous rock formation
• Lava cools to become
igneous rock
– Happens quickly when
exposed to air
– Darker color where already
started to crystallize
• Magma cools slowly
below Earth’s surface
– Can become exposed to
the Earth’s surface
eventually after wind, water
and other factors wear
away the ground on top of it
Extrusive rocks
• When volcanic
material erupts and
cools and crystallizes
on Earth’s surface
– Lava and ash solidify to
form this
– Happens fast= not
enough time for
crystals to grow
– Fine-grained texture
Extrusive rocks cont’d
• Volcanic glass=
rock that forms
when lava cools
too quickly to
form crystals
– Example:
Obsidian (both
pictures)
Extrusive rocks cont’d
• Gases can be trapped in
magma
– Magma moves towards
the surface
– Gases can cause
eruptions (think of
carbonation in soda)
• Gas-rich lava erupts and
gases escape
– Forms special igneous
extrusive rocks
– Example: pumice
• Why do you think pumice
has all those holes?
Mini Lab p.120
• I NEED 3 VOLUNTEERS
• Each Volunteer will receive 1 beaker and 1 watch
glasse
• Fill the three beakers with water
– One filled with HOT water
– One filled with WARM water
– One filled with COLD water
• Place the beakers in the back of the room
• Place one watch glass on each of the beaker
– MAKE SURE THERE IS ENOUGH WATER SO IT IS
TOUCHING THE WATCH GLASS
• I will come around and pour 3mL of water with
dissolved Epsom salt. We will look at the crystals
TOMORROW.
Intrusive rock
• Igneous rocks that
form as magma cools
slowly underground
– Large, well-defined
crystals can form
– Random arrangement
of crystals
• Crystals interlock like a
jigsaw puzzle
• Typical
characteristics:
– Large crystals
– Random arrangement
Igneous rock identification
• Texture:
– Crystal size
• Small + hard to see
(sometimes only
with magnifying
lens)= extrusive
• Large enough to
see with
interlocking
arrangement=
intrusive
Igneous rock identification
• Composition:
– Silica content (estimate
based on color of minerals)
• Darker colored minerals=
usually less silica and more
magnesium and iron
– Examples: Perodite contains
minerals olivine and pyroxene
• Lighter colored minerals=
usually more silica
– Examples: rhyolite contains
minerals quartz and feldspar
Igneous rock identification
Igneous rock identification
HOMEWORK Ch4 L.2
• Vocabulary words on Flash Cards
– MEMORIZE FOR QUIZ
• Outline Ch4 L.2
• Lesson review questions
– Page 123
– Questions 1-10
• QUIZ!!!!!
Ch4 L.3 Sedimentary Rocks
Bell Work Ch4 L.3
• Compaction: the weight from layers of
sediment forces out fluids and decreases
space between grains
• Cementation: Minerals dissolved in water
crystallize between sediment grains
• Clastic rock: Made up of broken pieces of
minerals and rock fragments
• Clast: the broken pieces of minerals and rock
fragments that form clastic rock.
• Chemical rock: form when minerals crystallize
directly from water.
• Biochemical rock: Sedimentary rock that was
formed by organisms or contains the remains
of organisms
Essential questions
• How do sedimentary rocks form?
• What are the three types of
sedimentary rocks?
Mini Lab Follow up
• What do you think crystals will look like?
• Write down your predictions. THEN go to the
back of the room and observe the crystals
formed from the three environments
– Hot, Warm, Cold
• Record your observations
– How are the crystals different?
Prediction Prediction Prediction Observation Observation Observation
(hot)
(warm)
(cold)
(hot)
(warm)
(cold)
Sedimentary rock formation
• Can form in different environments
– Water and air can break down rock
• Also can transport rock fragments to new locations
• Sediment deposited in layers
– Gets thicker over time
– Compaction: the weight from layers of sediment
forces out fluids and decreases space between grains
Sedimentary rock formation
cont’d
• Compaction can lead
to cementation
– Minerals dissolved in
water crystallize
between sediment
grains
• Holds grains together
• Examples of minerals
that cement: quartz,
calcite, and clay
Sedimentary rock
identification
• Classified according to how they
form
– Deposited, compacted then cemented
– Evaporation when minerals crystallize
from water
– When organisms remove minerals from
water to make shells or skeletons
Clastic Sedimentary Rocks
• Made up of broken pieces of
minerals and rock fragments
– Clasts= broken pieces
• Identify according to clast
shape and size
– Can’t use shape alone
• Can be as big as a car or as small
as a grain of flour
• Shape helps determine
environment where it formed
– Small, gritty sediment= typically
in calm environments (sea floor,
bottom of lake)
– Large sediment= can be moved
by oceans waves, fast flowing
rivers
Chemical sedimentary rock
• Dissolved minerals can be carried from
rivers to the ocean (contribute to saltiness)
• Water can be saturated with dissolved
mineral and minerals can crystallize out of
the water
• Chemical rocks form when minerals
crystallize directly from water.
Chemical sedimentary rock
cont’d
• Examples: rock salt
(halite), rock gypsum,
limestone
• Interlocking crystalline
texture (similar to
igneous rocks)
• Generally composed of
one dominant mineral=
uniform in color
– Different from igneous
rocks (generally many
minerals)= multi-colored
Biochemical sedimentary rocks
• Sedimentary rock that
was formed by
organisms or
contains the remains
of organisms
– Most common=
limestone
• Organisms make shells
from dissolved minerals
– Organism dies and
shells settle on the
floor= forms part of
rock
• If contains fossils=
fossiliferous
Biochemical sedimentary
rocks
• Carbonate rock= contains
carbon and oxygen
– Will fizz when add
hydrochloric acid
• Limestone is an example
– Not all biochemical rocks are
carbonates
• Diatomite looks like limestone
but doesn’t fizz with HCl
• Coal
– Composed of remains of
plants and animals
• Buried and compressed to
eventually form sedimentary
rock
Common Chemical and
Biochemical Rocks
Mini Lab p. 128
• Use grains of sedimentary rocks to identify the
environment where they likely formed
• What to look for? (Write this down for each)
– Grain size
– Grain shape
– Have you seen something similar before?
• Guess: in what environment was each formed?
Grain Size? Grain Shape? Seen this before?
#1
#2
#3
#4
Environment guess
HOMEWORK
• Vocabulary words on Flash Cards
– Memorize for quiz
• Ch4 L.3 Outline
• Lesson review questions
– Page 130
– Questions 1-10
• QUIZ
Ch4 L.4 Metamorphic Rock
Bell Work Ch4 L.4
• Metamorphism: any process that affects the
structure or composition of a rock in a solid state
as a result of changes in temperature, pressure or
the addition of chemical fluids
• Plastic deformation: permanent change in shape
by bending and folding
• Foliated rock: metamorphic rock that contains
parallel layers of flat and elongated minerals
• Contact metamorphism: Magma comes in contact
with existing rock, its thermal energy and gases
interact with the surrounding rock, forming new
rock.
• Regional metamorphism: Formation of
metamorphic rock bodies that are hundreds of
square kilometers in size
Essential questions
• How do metamorphic rocks form?
• How do types of metamorphic rocks
differ?
Metamorphic rock formation
• Metamorphism: any
process that affects
the structure or
composition of a rock
in a solid state as a
result of changes in
temperature, pressure
or the addition of
chemical fluids.
• Most metamorphic
rocks form deep
within the Earth’s
crust.
– Why?
Metamorphic rock formation
• Do not crystallize from
magma
– Different from igneous rocks
• Do not result from erosion
and deposition
– Different from sedimentary
rocks
• Rocks change shape
because of extreme
temperature and pressure
– Bend and twist into wrinkly
layers
Temperature and Pressure
• Under high temperature
and pressure, rocks
behave like bendable
plastic, they can bend or
fold
– Plastic deformation:
permanent change in
shape by bending and
folding
• Occurs during uplifting
events when techtonic
plates collide and form
mountains
– This is how the texture
changes
Temperature and Pressure
• Parent rock: rock that changes during
metamorphism.
– Temperature depends on composition,
between 150-200 degrees Celcius
Metamorphic rock identification
• Classified into two
groups based on texture
(foliated and nonfoliated)
– Changes in pressure can
align minerals to form
layers
• Can look like clastic
sedimentary rock
– BUT presence of crystalline
minerals in metamorphic
rock differentiate it from
sedimentary rock
– Rock can also have
blocky, interlocking
crystals that are uniform in
color
Foliated rocks
• Contain parallel
layers of flat and
elongated minerals
• Layering is because
of uneven
distribution of
pressure during
metamorphism
• Examples: phyllite
and gneiss
Nonfoliated rocks
• Metamorphic rocks that
have mineral grins with
a random, interlocking
texture
– No obvious alignment
– Individual crystals look
blocky and approximately
equal in size
• Minerals are generally
uniform in color
– Different from igneous
rock that is generally
multicolored (like granite)
• Examples: amphibolite
and quartzine
Contact metamorphism
• Magma comes in
contact with existing
rock, and its thermal
energy and gases
interact with the
surrounding rock,
forming new
metamorphic rock.
• Can increase crystal
size or form new
minerals and change
rock
Regional metamorphism
• Formation of metamorphic rock bodies that are
hundreds of square kilometers in size
• Changes in temperature and pressure and
presence of chemical fluids
– Can create entire mountain range of metamorphic rock
• Examples: Himalayas (Asia), Appalachian Mountains (US)
– Act on large volumes of rock
Metamorphic rocks
Rock identification lab
Crystal size?
Color?
Arrangement?
Special?
Igneous
Small (extrusive),
large (intrusive)
Multi-colored
Interlocking
(intrusive)
Light (silica),
dark (Fe3+,Mg2+)
Sedimentary
See pebbles or
grains but not
really crystals
Uniform color
Varies, can have
layering
Fossils?
Carbonate?
Metamorphic
Yes
Varies, can be
uniform
Nonfoliated (blocky,
interlocking
crystals=uniform
color)
Folliated (parallel
layers of
elongated
minerals)
Crystals
visible?
#1
#2
#3
#4
Single color or
multi-colored?
Uniform
size grains?
Layers?
What kind Rock
of rock?
Identification?
HOMEWORK Ch4 L.4
• Vocabulary words on Flash Cards
– MEMORIZE FOR QUIZ
• Outline Ch4 L.4
• Lesson review questions
– Page 137
– Questions 1-8
• QUIZ!!!!