Transcript How do rocks differ from minerals?

How do rocks differ from minerals?
• The physical properties of a mineral are
homogeneous (the same throughout the
sample)
• The physical properties of a rock are
usually heterogeneous (they vary
throughout the sample) because they’re
usually made up of several minerals
• Rocks are classified according to origin
(how they form)
These minerals
are all in this
rock
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
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
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
Classification of Sedimentary
Rocks
• We classify sedimentary rocks depending
on whether the sediments came from
– Particles of other rocks (“land derived”)
– Ions that have precipitated out of seawater
(“chemically derived”)
– Living organisms (“organically derived”)
Sand Composition Varies BUT TO BE
CONSIDERED SAND THE GRAIN SIZE IS
BETWEEN 0.2 -0.006 CM.
Sedona Sandstone
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
Shale
Source: Photograph © The McGraw-Hill Companies, Inc./Bob Coyle, photographer.
Sandstone
Source: Photograph © The McGraw-Hill Companies, Inc./Doug Sherman, photographer.
2 TYPES OF TEXTURE
 CRYSTALLINE FOR CHEMICALLY
FORMED SEDIMENTARY ROCKS
 BIOCLASTIC FOR ORGANICALLY
FORMED SEDIMENTARY ROCKS
 HOW USEFUL IS GRAIN SIZE????
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
 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 taken out of solution by
marine organisms for their hard parts (shells)
can 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 ( bubbles with
acid)
COAL
• Decayed plant remains
BIOCLASTIC LIMESTONE
COAL
CHEMICALLY PRECIPITATED
LIMESTONE
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Summary
 Inorganic Land-Derived Sedimentary
Rocks are identified by Texture or Grain
Size
Chemically and/or Organically Formed
Sedimentary Rocks are identified by
Composition
What conditions control which
Sedimentary Rock is formed?????
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
SALT AND GYPSUM
EVAPORATION
 Bedrock of Salt and Gypsum around
Buffalo
 What type of environment would cause
salt and/or gypsum to evaporate?
 Ocean environment with hot temperatures
CHARACTERISTICS OF
SEDIMENTARY ROCKS
1. Horizontal layers called beds or strata
2. Clasts are rounded and sorted because
they have been moved by water
3. Ripple Marks
4. Mud Cracks
5. Fossils
6. Interconnected mineral crystals of 1
mineral (monominerallic)
HORIZONTAL LAYERS
A. SHALLOW WATER B. LOW ENERGY C. DIRECTION OF FLOW
MUDCRACKS
ALTERNATING WET AND DRY
CONDITIONS
Limestone - FOSSILS
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
Formation of Igneous Rocks
COOLING AND
SOLIDIFICATION OF
MAGMA/LAVA
INTERGROWN OR
INTERCONNECTED
SILICATE
CRYSTALS IN A
RANDOM PATTERN
– NOT ORGANIZED
IGNEOUS ROCKS ARE
CLASSIFIED BASED ON 2 MAIN
CHARACTERISTICS
• TEXTURE – MINERAL GRAIN SIZE
• MINERAL COMPOSITION
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
ESRT – TOP OF THE IGNEOUS
ROCK SCHEME TELLS THE
TEXTURE / GRAIN SIZE
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.
What does granite bedrock exposed at the surface
indicate?
COOLING HISTORY / GRAIN
SIZE ALONE
CANNOT NAME THE ROCK
WE NEED TO KNOW
COMPOSITION
TEXTURE + COMPOSITION =
ROCK CAN BE IDENTIFIED
THE BOTTOM OF THE IGNEOUS ROCK
SCHEME TELLS YOU THE COMPOSITION
TEXTURE + COMPOSITION CAN NAME ROCK
Igneous Rocks Consist of 7 Silicate Minerals
Quartz
Potassium feldspar
Plagioclase feldspar
Biotite mica
Amphibole
(hornblende)
Pyroxene
Olivine
NO SINGLE IGNEOUS ROCKS IS MADE UP
OF ALL 7 MINERALS
FELSIC VS. MAFIC
FELSIC
MAFIC
“FEL” = FELDSPARS
“MA” = MAGNESIUM
“SIC” = SILICA
“F” = IRON
High % of quartz,
feldspars, mica
“IC” = SILICA
High % of pyroxene,
feldspars, amphibole
DARKER IN COLOR
LIGHTER IN COLOR
LESS DENSE
FELSIC
COMPOSITION
COLUMN
+
COARSE
TEXTURE
ROW
IGNEOUS ROCK COMPOSITION
FELSIC ROCKS – 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
IGNEOUS ROCK COMPOSITION
INTERMEDIATE ROCKS
MIXED FELSIC/MAFIC
MIXED CRUST
ANDESITE (named for Andes
Mountains) – fine-grained
2nd most abundant volcanic
rock in Earth’s crust.
DIORITE – coarse-grained
IGNEOUS ROCK COMPOSITION
ULTRAMAFIC ROCKS – form from magma in
ASTHENOSPHERE
Dominated by Fe-Mg silicates, olivine and pyroxene.
Very dark in color and dense
Found at converging continental
plate boundaries.
Peridotite
Dunite
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
Lava Field at Sunset Crater
WHAT GRAPH BELOW SHOWS AS
TIME INCREASES THE SIZE
INCREASES?
A
B
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 (but not
high enough to melt!)
• 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 (see page 10
ESRT)
 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
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
Classification of Regional
Metamorphic Rocks
 Composition is basically the
same for all foliated rocks –
parent rock is usually listed in
comments section.
 Type of texture and grain size
determined by the amount of heat
and pressure
GRADES OF METAMORPHISM
LOW GRADE – LESS HEAT AND PRESSURE – SLATE
HIGH GRADE – MORE HEAT AND PRESSURE - GNEISS
Temperature
Low-grade metamorphism:
Occurs at about 2000 C to 5000 C.
and pressure greater than 1,000
atmospheres
High-grade metamorphism:
Occurs at > 5000 C
FOLIATED METAMORPHIC ROCKS
MICA SCHIST WITH GARNET
MICA
CRYSTALS
BECOME
LARGE
AND
SPANGLY
Grand Teton Gneiss
METAMORPHIC ROCKS WILL
OFTEN BE DEFORMED
BECAUSE OF INTENSE HEAT
AND PRESSURE
LOOK AT ROCK SYMBOL FOR GNEISS
A metamorphic rock exposed
to too much heat will melt
and become ???
MAGMA
 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? Sandstone??
PARENT ROCK IN THE COMMENTS
LIMESTONE METAMORPHOSES INTO MARBLE
SANDSTONE METAMORPHOSES INTO QUARTZITE
Rock Classification Summary
• If the rock looks “dirty” or contains fossils,
it’s sedimentary
• If the rock shows banding or folds or twists
or mineral alignment, it’s metamorphic
• If the rock is glassy or contains rounded
crystals or gas pockets, it’s igneous
Rock Distribution
• Sedimentary rocks are at or near the
Earth’s surface because they require
water to form
• Igneous rocks are found near volcanoes
and deep underground.
• Metamorphic rocks are found deep within
mountains, deep underground, and at
transition zones between sedimentary and
igneous rocks
ANY TYPE OF ROCK CAN BE CHANGED INTO ANY OTHER TYPE OF ROCK