Download Rocks ISM 22 2014 - AlmaMiddleSchoolScience

Rocks Tell Stories
Records of Geologic Past
Rock Classification – 3 major
groups based on their methods of
formation or origin
1. Igneous rocks … from cooling and
solidification of lava or magma
2. Sedimentary rocks … from compacted
and cemented sediments, or chemical
precipitates or evaporites
3. Metamorphic rocks …
meta (change) morphic (form) …
rocks changed by heat and pressure –
but remain solid
IGNEOUS ROCKS
MAGMA VS. LAVA
Magma – molten material
BELOW the surface of the
Earth
Lava – molten material
AT OR ABOVE earth’s
surface
ENVIRONMENT OF FORMATION
COOLING HISTORY
MAGMA
LAVA
Intrusive – below the surface
Extrusive - above the surface
A pluton is a body or
chamber of magma deep
inside the crust.
Ejected from volcano
Rocks formed when magma
Rocks formed when lava
cools and solidifies are called cools and solidifies are called
INTRUSIVE (PLUTONIC)
EXTRUSIVE (VOLCANIC)
EXTRUSIVE FEATURES
VOLCANO - landforms generated when lava is
released from the Earth’s interior through
openings.
Magma Intrusive
Features - Plutonic
IGNEOUS ROCKS ARE
CLASSIFIED BASED ON 2 MAIN
CHARACTERISTICS
• TEXTURE – MINERAL GRAIN SIZE
• MINERAL COMPOSITION
Classification of Igneous Rocks
by Texture
• WHAT IS TEXTURE?
It is not how it feels
SIZE OF MINERAL CRYSTALS
What controls texture?
How fast an igneous rock
cools.
What controls how fast an igneous
rock cools?
Where the rock is formed.
slower cooling
coarser crystals
deep in ground
Classification of Igneous Rocks –
Texture or Grain Size
Extrusive
Extrusive
Intrusive
Intrusive
Volcanic LAVA
VolcanicLAVA
Plutonic MAGMA
Plutonic MAGMA
Extremely
fast cooling
Fast Cooling
Slow
Cooling
Extremely
slow cooling
NonFine-grained
crystalline
Glassy
vesicular (gas
pockets)
Coarsegrained
Very Coarsegrained
EXTRUSIVE – VOLCANIC - LAVA
• When lava cools extremely fast crystals have
no time to form – JUST FROZEN IN PLACE
RANDOMLY WHEN LAVA ENTERS
ATMOSPHERE OR WATER
• GLASSY – NON-CRYSTALLINE
Non-vesicular
Vesicular
gas pockets
EXTRUSIVE – VOLCANIC - LAVA
Lava that cools fast at or near the Earth’s
surface
Produces small crystals
FINE-GRAINED TEXTURE
not easily seen with the naked eye.
INTRUSIVE – PLUTONIC - MAGMA
Magma that cools slowly deep underground
produces large crystals
COARSE-GRAINED TEXTURE
easily seen with the naked eye.
INTRUSIVE – PLUTONIC - MAGMA
EXTREMELY SLOW COOLING HAS
ABNORMALLY LARGE CRYSTALS
AND IS VERY COARSE.
IGNEOUS ROCK MANTRA
• INTERGROWN CRYSTALS IN A
RANDOM PATTERN FOR ALL
ROCKS EXCEPT:
NO CRYSTALS
• OBSIDIAN – GLASSY
• PUMICE, SCORIA, VESICULAR
BASALT – GAS POCKETS OR
VESICULAR
IGNEOUS ROCK COMPOSITION
CONTINENTAL CRUST
GRANITE – coarse-grained
(continental crust)
RHYOLITE – fine-grained
OBSIDIAN - glassy and
PUMICE - porous (vesicular).
PEGMATITE - very coarse-grained
IGNEOUS ROCK COMPOSITION
MAFIC ROCKS –OCEANIC CRUST
GABBRO – coarse-grained
BASALT – fine-grained
(ocean crust)
SCORIA – vesicular (gas pockets)
VESICULAR BASALT – vesicular
INTRUSIVE
EXTRUSIVE
Granite
Rhyolite
Figure 4.7
A
MINERAL
COMPOSITION
THE SAME – TEXTURE ONLY
DIFFERENCE
Intrusive vs. Extrusive
INTRUSIVE
EXTRUSIVE
MINERAL COMPOSITION THE SAME ---- TEXTURE
ONLY DIFFERENCE
Andesite
Diorite
Intrusive vs. Extrusive
INTRUSIVE
Gabbro
EXTRUSIVE
Basalt
MINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE
Intrusive vs. Extrusive
WHAT GRAPH BELOW SHOWS AS
TIME INCREASES THE CRYSTAL
SIZE INCREASES?
A
B
VOLCANISM
Has produced most of the water
on Earth.
Has vastly modified the Earth’s
atmosphere.
Has created new land.
Produces fertile agricultural land.
Provides a source of geothermal
energy in Iceland and California.
Presents significant natural hazard.
VOLCANOES AND VOLCANISM
The Nature and Status of Volcanoes
EXTINCT - has not erupted in very long time,
generally > 10,000 years.
Shiprock, New Mexico
VOLCANOES AND VOLCANISM
The Nature and Status of Volcanoes
DORMANT - has not erupted in past 2000-3000 years,
but has potential to erupt.
Mt. Baker, WA
Chiliques volcano in Chile.
VOLCANOES AND VOLCANISM
The Nature and Status of Volcanoes
ACTIVE - currently erupting volcano or one that
has erupted recently.
Mt. Lassen, CA
Kilauea, HI
Explosive vs Non-explosive
VOLCANOES AND VOLCANISM
Mt. St. Helens, WA
17 May 1980
VOLCANOES AND VOLCANISM
Mt. St. Helens, WA
18 May 1980
VOLCANOES AND VOLCANISM
Mt. St. Helens, WA
19 May 1982
SEDIMENTARY ROCKS
Sedimentary Rocks
• 80 % of Earth’s surface is covered
with sediments and Sedimentary
Rocks
What is sediment????
 Broken pieces of rocks called CLASTS
 Chemical precipitates ( dissolved solids
come out of solution)
 Organic fragments – shells, decayed
plant matter – this is called BIOCLASTIC
Source of Sediment
When Igneous, Metamorphic Rocks, and
Sedimentary Rocks are uncovered and exposed
to the atmosphere and hydrosphere they start to
break down
Weathering is the general term for all actions
that break down or wear away rock
Erosion is the carrying away of the sediment
Sedimentary Rocks form when
sediments/clasts are transported to
large bodies of water and are …
Deposited in horizontal layers
called beds or strata
Buried
Compacted – particles forced
extremely close together because
of the pressure of the overlying
layers and water
Cemented – glued together
Sedimentary Rocks
Sediments that are
eroded settle to the
bottom of the rivers,
lakes, and oceans
Layer after layer of
eroded earth is
deposited on top of
each other
Cementing Material (Glue)
•
Minerals precipitate out of solution to
cement particles together.
Cementing material is often quartz, calcite, and hematite
Most Sedimentary Rocks form
under large bodies of water, such
as lakes, seas, and oceans
Horizontal layers deposited under water
E
D
C
B
A
Future index
fossil!
According to the law of
Super position which
layer is the oldest?
Classification of Sedimentary
Rocks
• We classify sedimentary rocks depending
whether the sediments are
LAND DERIVED (came from)
CHEMICALLY - ORGANICALLY DERIVED
INORGANIC LAND DERIVED
 Main source of clasts are from pre-
existing igneous, metamorphic or
other sedimentary rocks that have
been weathered.
Sand Composition Varies BUT TO BE
CONSIDERED SAND THE GRAIN SIZE IS
BETWEEN 0.2 -0.006 CM.
Sediments
are
pebbles,
cobbles,
and
boulders
rounded
Breccia
angular
Silt (0.006 to 0.0004 cms.
SILTSTONE
Sand (0.2 to 0.006 cms.)
SANDSTONE
Clay (less than 0.0004 cms.)
SHALE
CHEMICAL Sedimentary Rocks
Sediment From Solution
 All liquid water contains dissolved
minerals.
 These minerals precipitate (dissolved
solids come out of solution/water)
 Usually happens because of evaporation
Characteristics of Chemically
Formed Sedimentary Rocks
They are monominerallic –
consisting of intergrown
crystals of just 1 mineral.

 Form in shallow seas
ROCK SALT
Intergrown
crystals of just
1 mineral
DOLOSTONE
ROCK GYPSUM
ORGANIC Sedimentary Rocks
Bioclastic Sediment
LIMESTONE AND CORALS
•
Dissolved minerals (CaCO3) taken out of solution by marine
organisms for their hard parts (shells) pile up on the seafloor
when they die.
•
These fossil remains accumulate into a thick enough layer to form
an “organic” sedimentary rock
•
Cement is commonly calcite ( Test = bubbles with acid)
COAL
•
Decayed plant remains
•
Peat->
•
Lignite->
•
Bituminous->
•
Anthracite->
•
Crude Oil->
•
Natural gas
BIOCLASTIC LIMESTONE
COAL
(Bituminous)
CHEMICALLY PRECIPITATED
LIMESTONE
LIMESTONE
forming
THE SIZE OF THE GRAIN IS
DETERMINED BY THE
ENVIRONMENT OF FORMATION
 HIGH ENERGY ENVIRONMENT
Large particles
Fast moving water – rivers, ocean waves
 LOW ENERGY ENVIRONMENT
Small particles
Slow moving water – lake, bay, swamp
SEDIMENTARY
ROCK
WHERE IT WAS
PUT TOGETHER
CONGLOMERATE
BRECCIA
HIGH ENERGY
SANDSTONE
MEDIUM ENERGY
SILSTONE
LOW ENERGY
SHALE
VERY LOW ENERGY
Environment of Formation
Ocean Derived Sedimentary Rocks
Sedimentary Rocks
help us understand our past
geologic history
There is evidence of climate
change as well as lost species
of plants and animals in
Sedimentary Rocks
During the
Cretaceous Period
(about 120 mya) a
shallow inland sea
split North
America.
We know this by
the Sedimentary
Rocks deposited
in the former
shallow sea
Cretaceous Limestone Deposits in Kansas
HORIZONTAL LAYERS
MUDCRACKS
ALTERNATING WET AND DRY
CONDITIONS
Limestone - FOSSILS
SEDIMENTARY ROCK MANTRA
1.COMPACTED AND
CEMENTED SEDIMENTS
FOSSILS
RIPPLE MARKS
MUDCRACKS
METAMORPHIC ROCKS
METAMORPHIC ROCKS
META = CHANGE
 Called
MORPH = FORM
the “Cinderella Rock”
 Start with pre-existing rock
and change to another rock –
but these changes occur in the
SOLID STATE
METAMORPHISM
 Process
by which igneous,
sedimentary, or another
metamorphic rock called the
“parent rock” undergoes
changes in minerals and
texture
METAMORPHISM
Occurs in rocks due to the
effects of
• High temperature
• High pressure
HEAT EFFECTS
Temperature increases with depth or
contact with magma
 Recrystallization – a process that
forms new mineral crystals because
the mineral is no longer stable at the
new temperature

• Changes to a new (high temperature)
mineral
PRESSURE EFFECTS
 Pressure increases with depth –
weight of overlying rock
 Mineral crystals grow larger
 Mineral crystals are more dense
 Mineral crystals grow perpendicular
to pressure
 Mineral crystals are arranged in
parallel layers – PRODUCES
FOLIATION
FOLIATION
 Pressure actually rearranges the minerals
into parallel layers.
 More pressure – minerals grow larger and
recrystallize and separate into layers
 Even more pressure – alternating layers of
light and dark minerals called
Banding
Random
arrangement
of minerals
Organized
arrangement of
minerals - banding
METAMORPHIC ROCK MANTRA
• INTERGROWN CRYSTALS
IN AN ORGANIZED
PATTERN
Granite
Intergrown crystals
random pattern
Gneiss
Intergrown crystals
Organized Pattern
2 Types of Metamorphism
1. Regional Metamorphism – Occurs over
large areas where there is active
mountain building
a) Convergent plate boundaries
2. Contact Metamorphism – areas in
contact with magma intrusions and/or
lava extrusions
MOUNTAIN
BUILDING
GRADES OF METAMORPHISM
LOW GRADE – LESS HEAT AND PRESSURE – SLATE
HIGH GRADE – MORE HEAT AND PRESSURE - GNEISS
FOLIATED METAMORPHIC ROCKS
METAMORPHIC ROCKS WILL
OFTEN BE DEFORMED
BECAUSE OF INTENSE HEAT
AND PRESSURE
LOOK AT ROCK SYMBOL FOR GNEISS
DEFORMED GNEISS
A metamorphic rock exposed
to too much heat will melt
and become ???
MAGMA
CONTACT METAMORPHISM
Contact Metamorphic
• Metamorphism
means "changed
form".
• The Changes occur
because of:
• Heat from magma
intruding on the
surrounding rock
• Very little pressure
 Near magma chambers (plutons)
 Rocks in “contact” with the
magma are baked
 New minerals are formed –
recrystallization
 Transition zone of contact
metamorphism is usually relatively
narrow baking the adjacent rocks
Contact Metamorphism – Baking
the adjacent rocks
Symbol for Contact Metamorphism
is a line with tick marks
When limestone undergoes contact
metamorphism what rock will it metamorphose
into? Marble!
PARENT ROCK IN THE COMMENTS
LIMESTONE METAMORPHOSES INTO MARBLE
SANDSTONE METAMORPHOSES INTO QUARTZITE