Download Origin of Rocks

Origin of Rocks
• Rocks are classified by the way
they are formed.
• Igneous rocks: formed from the
cooling of molten rock.
• Sedimentary rocks: formed from
sediments being compacted and
cemented.
• Metamorphic rocks: existing
rock that is changed by heat,
pressure, or chemical reactions.
Igneous Rocks
• Classified by
origin, texture
(crystal size),
and mineral
composition.
• From the Latin
word “ignis,”
which means
fire.
Extrusive Igneous Rock
 Extrusive rock is formed
from lava that erupted
on the surface and
rapidly cooled. Will have
tiny crystals, be very
fine grained, and
sometimes even appear
glassy.
 Basalt is most common
of this type.
Basalt Forming
What type of lava is this? How do you know?
Intrusive Igneous
Rock
• Forms when
magma cools
underground.
• Usually cools
slowly, so it will
have large
crystals and be
coarse grained.
• Granite is most
common intrusive
rock.
Explain This!
• How would you
explain an intrusive
rock that had both
large and small
crystals?
• It must have cooled
slowly at first, then
cooled more rapidly
as it got closer to
the surface.
Porphyritic Rock
• Deep underground
the heat cannot
dissipate as
rapidly, so the rock
cools slowly. Near
the surface the
heat can escape
into the air, so it
cools rapidly.
Metamorphic
Rocks
• “Meta” is ancient
Greek for change.
• “Morph” is ancient
Greek for form.
• Metamorphic rock
then is rock that
has changed from
one form to
another.
How
Metamorphic
Rocks Form
• Deep below the Earth’s
surface the intense
heat and pressure can
change rocks.
• Their appearance,
texture, crystal
structure and mineral
content can change.
• Fossils will be
destroyed.
How Does Metamorphism Happen?
CONTACT
metamorphism:
• Rocks are heated by
contact with
magma/lava
• Affects small areas
• Usually occurs along
the edges of igneous
intrusions
How Does Metamorphism Happen?
REGIONAL
metamorphism
– Rocks deeply buried
are changed by
heat and pressure
– Affects large areas
– Often occurs along
plate boundaries
• These rocks started out as some other type
of rock, but have been greatly changed
from their original igneous, sedimentary, or
earlier metamorphic form.
• Metamorphic rocks form when rocks are
subjected to high heat, high pressure, hot,
mineral-rich fluids or, more commonly,
some combination of these factors.
Metamorphic Changes
Almost melted!
• Metamorphic rocks are
often squished,
smeared out, and
folded.
• Despite these
conditions,
metamorphic rocks do
not get hot enough to
melt, or they would
become igneous rocks.
Classifying Metamorphic Rock
• Classified by the
arrangement of the
grains.
• Foliated
• Non-foliated
Foliated Metamorphic Rock
• Grains are in
parallel layers or
bands.
• “Foliated” is the
Latin word for leaf.
• Describes the thin
layering found in
many metamorphic
rocks.
• These rocks will
split along these
bands.
Slate
• Formed when shale
is subjected to
pressure.
• Denser, more
compacted than
shale.
• Produces flat plates
when broken.
Slate to Schist
• If slate is subjected
to even greater
pressure and
moderate
temperatures,
schist is formed.
Granite to Gneiss
• Granite becomes
gneiss when
subjected to heat
and pressure.
• The atoms end up
lining up in bands.
Non-foliated Metamorphic Rock
• Mineral grains are
randomized.
• Do not split into
layers.
• Usually smoother
and denser than
the parent rock.
Quartzite
• Occurs when
sandstone is
compressed by
pressure.
• Usually very hard.
• Formed from
metamorphed
limestone.
• Much harder and
denser.
Marble
Origin of Rocks
• Rocks are classified by the way
they are formed.
• Igneous rocks: formed from the
cooling of molten rock.
• Sedimentary rocks: formed from
sediments being compacted and
cemented.
• Metamorphic rocks: existing
rock that is changed by heat,
pressure, or chemical reactions.
Sedimentary Rocks
• Formed from
particles deposited
by wind and water.
• Sediment is small
pieces of solid
materials that
come from rocks or
living things.
• What do these
rocks have in
common?
Stratification
• These rocks are
layered or
“stratified.”
• This feature is also
called “Bedding”
Weathering, Erosion, Transportation
• Occurs when water,
wind, ice,
chemicals, or
organic processes
loosens rock and
soil and some
mechanism carries
it away.
Deposition
• The process by
which the sediment
settles out of the
water or air
carrying it.
• Sediment is
deposited when the
wind or water
speed decreases.
Graded Bedding
• Explain how this could have occurred.
Graded Bedding
• Explain this.
Cross Bedding
Wind-deposited cross bedding
Water-deposited cross bedding
Explain these.
Ever see these before?
Formation of Ripple Marks
What are these?
What are these?
Burial and Compaction
• As the sediments settle they will loosely fit on
top of each other.
• As the years go by, more and more sediment is
added.
• The bottom layers get compacted by the weight
of the layers above them.
• Water is often squeezed out.
Cementation
 While compaction is going
on, minerals in the rock
slowly dissolve.
 The dissolved minerals
seep into the spaces
between the compacted
sediment as the water is
squeezed out.
 They crystallize and glue
the sediments together.
Lithification
• The process by which
sediment becomes
sedimentary rock.
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Weathering
Erosion
Transportation
Deposition
Burial
Compaction
Cementation
Types of sedimentary rocks
• Clastic: sediments made of broken fragments
• Coarse-grained rocks-fast moving water,
rockfalls, landslides.
• Medium-grained rock: streams, rivers,
shorelines.
• Sandstone, arkose
Fine-grained rocks
• Shale, siltstone, mudstone
• Ponds, swamps
• very slow-moving water
Chemical and Biochemical sedrocks.
• Chemical
– Precipitates-rocks that have a sediment derived
from minerals that have precipitated out of a
solution.
– Calcareous Tufa, Chemical Limestone, stalagmites
and stalactites.
– Evaporites-water that contains dissolved minerals
evaporate and leave behind the minerals which
can accumulate at the bed.
– Halite, gypsum, some types of limestone
Biochemical
• Rocks formed from the remains of living
organisms.
• Coquina
• Bituminous coal
• Fossiliferous limestone
• Certain types of chalk