Chapter 6 Rocks
CornellCh.Notes-Pg.
32
6 Rocks
Purpose
To learn about the world around
us, and how this dynamic and
changing world affects society.
Essential Question
How are rocks formed, and how do they
change over time to look like what we see
all around us today?
What is a Rock?
• Rocks = Naturally-occurring
mixtures of minerals,
mineraloids, glass or organic
matter.
• Mineraloid=opal,
Amber, coal, etc.
• What is the difference
between a rock and a mineral?
–Rocks are made up of ONE
or MORE minerals.
–A rock can have once-living
material in it.
• Rocks are continually changed by
many processes, such as
weathering, erosion, compaction,
cementation, melting, and cooling.
• Rocks can change to and from the
three types:
1. Igneous
2. Sedimentary
3. Metamorphic
What is the process through
which rocks change?(Write now)
• The Rock Cycle—the process through
which earth materials change back
and forth among the different types
of rocks.
Igneous
rock
Metamorphic
rock
Sedimentary
rock
Igneous rock
Sedimentary
rock
IGNEOUS
Heat and
Pressure
Melting,
Solidification
Weathering,
Erosion,
Compaction,
Cementation
Weathering,
Erosion,
Compaction,
Cementation
Melting,
Solidification
SEDIMENTARY
METAMORPHIC
Heat and
Pressure
Chapter 6 Rocks
Cornell
Notes
Ch. 6 Rocks
Igneous Rocks
What are the types of
rocks?
• IGNEOUS
• SEDIMENTARY
• METAMORPHIC
• Rocks are divided into 3
groups based on how
they were formed
• “Ignis” = Latin for “fire”.
• Formed from the cooling of either
magma or lava.
• The most abundant type of rock.
• Classified according to their origin
and composition.
ORIGIN— Where rocks are formed
• 1. Below ground = from magma- forms
intrusive igneous rock.
• Usually have LARGE crystal grains (they cooled
slowly)
• 2. Above ground = from lava- forms
extrusive igneous rock
• Usually have SMALL or NO crystals (they
cooled too quickly)
COMPOSITION—
What kind of
substances the rocks are made of.
Some have large & small crystals (called
porphyritic)
Peridotite: Intrusive or
Extrusive? Why?
Granite: Intrusive or Extrusive?
Why?
Porphyry: Intrusive or Extrusive?
Why?
Obsidian: Intrusive or Extrusive?
Why?
Chapter 6 Rocks
Cornell
Notes
Ch. 6 Rocks
Sedimentary Rocks
• Formed from sediments
that are pressed or
cemented together.
• Sedimentary rocks
represent 7% of the
Earth’s crust,
• but they cover 70% of
the Earth’s surface.
• Sediments are Rock
fragments, mineral grains,
plant & animal remains.
• Water or wind breaks down
rock into sediments.
• These sediments are moved by wind,
water, ice or gravity.
• Then they are deposited (dropped)
What turns sediments into solid rock?
• Compaction=The heavy sediments press down on
the layers beneath causing the sediments to
fuse together.
• Cementation=Dissolved minerals flow
between the particles and cement them
together.
Chapter 6 Rocks
Cornell
Notes
Ch. 6 Rocks
Metamorphic Rocks
• Rocks that have changed due to intense
temperature and pressure
• “Meta” means “change” and morphosis
means “form” in Greek
• Igneous, sedimentary and other
metamorphic rocks can change to
become metamorphic rocks
What occurs in the Earth to
change these rocks?
• Pressure from overlying rock layers
• High heat, but not enough to melt the rock
• Rocks may be flattened or bent or atoms may be
exchanged to form new minerals.
How are metamorphic rocks classified?
• Foliated—mineral
grains are flattened
and line up in parallel
bands
– Example: gneiss
formed from
rearrangement of
minerals in granite
into bands
How are metamorphic rocks classified?
• Non-Foliated—No bands are formed
– Example: marble formed from limestone
Where do metamorphic rocks
usually form?
• Where magma intrudes
relatively cool rock
• Near colliding plates (near
mountain ranges)
• Places that are covered miles
thick with other rock causing
pressure
• When hot water intrudes rock
• Where a meteorite strikes
Earth (rare)
• Where lightning bolts strike
rocks (rare)
Chapter 6 Rocks
Cornell
Notes
Ch. 6 Rocks
Review
Rock Identification Characteristics
Fine Grain
• Smooth appearance
• In igneous and
metamorphic rock=no
or very small crystals
• Sedimentary rock=small
particles
Coarse Grain
• Rough or grainy
appearance
• In igneous and
metamorphic
rock=larger crystals
• Sedimentary
rock=larger particles
Course grained sedimentary rock
Coarse grained igneous rock
Coarse grained metamorphic rock
Fine grained sedimentary rock
Fine grained igneous rock
Fine grained metamorphic rock
Metamorphic Rock
Foliated-minerals arranged in
bands.
Unfoliated-minerals not
banded.
In: Pg.37
On the next slide are 4 metamorphic rocks. Tell
me if they are foliated or unfoliated.
1.
2.
3.
4.
1
3
2
4
Out
The 3 types of
rock are igneous,
sedimentary and
metamorphic.
1. What type of
rock is this?
2. How do you
know?