Rocks

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• Rocks

Igneous, Sedimentary, and Metamorphic
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Thought Question

• What are rocks? How are rocks different than
  minerals?
• Explain and diagram (draw it) the rock cycle.
• How do rocks form?

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Objectives

• Identify the three major types of rocks explain
  how each is formed
• Summarize and diagram the steps of the rock cycle
• Describe how the cooling rates of magma and lava
  affect the texture of igneous rocks
• Classify Igneous rocks according to their
  composition and specific rock structures
• Explain how rocks melt and crystallize discuss
  the factors that affect these rates.
• Classify the different types and textures of
  igneous rocks
• Discuss some common uses for igneous rocks

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THREE Rock Types

• Igneous- form when magma or lava cools can occur
  in or on the earths crust
• Magma-melted rock in the Earths surface
• Lava-melted rock that flows on the Earths
  surface
• Sedimentary-the deposition of broken down
  minerals, rocks, or organic matter that is
  hardened, cemented or compressed into rock
• Sediment-broken down minerals, rocks or organic
  material
• Metamorphic- rocks (igneous or sedimentary) that
  are changed by heat and/or pressure and/or
  chemical processes rocks that are chemically
  different from their parent material

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Igneous Rock Structures

• Intrusive Igneous Rocks- Any rock that forms
  beneath the earths surface/ underground usually
  has visible/large crystals can be meters thick or
  can be several of kilometers thick
• Batholiths Stock Laccoliths Sills and Dikes

• Extrusive Igneous Rocks- Any igneous rock that
  forms on the surface of the earth usually has
  small, crystals not visible to the naked eye
  (lava pyroclastic material)
• Volcanic Neck Lava Plateau/field Bombs Ash

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The Rock Cycle

• Rock Cycle- the geologic process that cause rocks
  to change from one form to another and back
  again

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A rock is a hard material made of one or more
minerals
Or anything that when you pick it up and throw it
at someone it produces the reaction "Owww! Why
did you hit me in the head with a rock?" A
rock can be made of only one mineral entirely
(monomineralic) or a mixture of many minerals
(polymineralic)
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3 groups of rocks

• A rock is a group of minerals joined together in
  some way
• Igneous formed by the cooling solidification
  of molten rock (magma)
• Sedimentary formed by the compaction
  cementation of layers of sediment (rock
  fragments, organic remains, chemical deposits)
• Metamorphic formed when existing rocks are
  CHANGED by intense heat pressure

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Igneous Rocks

• ESRT page 6

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Igneous rocks form from the cooling or
SOLIDIFICATION of magma (melted rock) The
RECRYSTALLIZATION of minerals is evident in
Igneous Rocks
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LIQUID HOT MAGMA

• Magma is a mixture of liquid rock, crystals, and
  gas
• It is characterized by a wide range of chemical
  compositions, with high temperature, and 
  properties of a liquid
• Magmas are less dense than surrounding rocks, and
  will therefore move upward

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Grain Size

• Cooling Rates
• When lava flows on Earths surface, it cools
  quickly and there is not enough time for large
  crystals to form.
• Extrusive igneous rocks have no visible mineral
  grains.
• When magma cools slowly beneath Earths surface,
  there is sufficient time for large crystals to
  form.
• Intrusive igneous rocks may have crystals larger
  than 1 cm.

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Igneous Rock Samples
Intrusive Granite www.windows.ucar.edu
Extrusive Lava Flow-McGraw Hill Pub.
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• If magma makes it to the surface it will erupt
  and later crystallize to form an extrusive or
  volcanic rock
• If it crystallizes before it reaches the surface
  it will form an igneous rock at depth called a
  plutonic or intrusive igneous rock
• Because cooling of the magma takes place at a
  different rate, the crystals that form and their
  texture exhibit different properties

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Large or Small Crystals?

• Texture- the appearance of a rock based on how
  visible the crystals/minerals in a rock are
• Coarse Grain- large visible crystals easily seen
  by the naked eye
• Fine Grain- small crystals that would only be
  visible with a powerful hand-lens or microscope
• Porphyritic- the mixture of large and small
  crystals

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intrusive igneous rocks

• Form by the cooling of magma UNDERGROUND
• IN trusive
• Also known as PLUTONIC

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• Underground cooling is SLOWER
• Rock crystals are LARGE have a coarse texture

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Composition and Origin of Magma

• Magma is a mix if molten rocks, dissolved gases,
  and minerals.
• Classified based on the amount of Silicates
  (SiO2) found in the magma three major types
• Rhyolitic- 70 SiO2 (usually light in color)
• Andesitic- 60 SiO2 (intermediate in color)
• Basaltic- 50 SiO2 (dark in color)

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Examples of Igneous Rx
Two Varieties of Granite
Fine Grain Basalt
Granite Porphyry
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Magma Formation

• Four major factors that affect the formation of
  magma are
• Temperature-different types of rocks melt at
  different temperatures (increases with depth)
• Pressure-the greater the pressure, the higher the
  melting point (increases with depth)
• Water Content-the addition of water tends to
  lower the melting point of most rocks
• Mineral Content-different minerals melt at
  different temperatures
• Silica content affects melting temperature and
  also impacts how quickly magma flows.

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For rocks to melt, the right combination of
temperature, pressure, and composition must be
present.
In general, oceanic crust is rich in iron and
magnesium and therefore melts at higher
temperatures than continental crust, which
contains higher levels of silicon and aluminum.
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Origins of Magma

• In the laboratory, most rocks must be heated to
  temperatures of 800C to 1200C before they melt.
  
• These temperatures are found in the upper mantle
  and lower crust.
• Scientists theorize that the remaining energy
  from Earths molten formation and the heat
  generated from the decay of radioactive elements
  are the sources of Earths thermal energy.

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• Granites higher water content and mineral
  composition cause it to melt at a lower
  temperature than basalt.

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How Rocks Melt-

• Partial melting is the process whereby some
  minerals melt at low temperatures while other
  minerals remain solid.
• Occurs because different minerals have different
  melting points not all parts of a rock melt at
  the same time.
• If temperatures are not great enough to melt the
  entire rock, the resulting magma will have a
  different chemistry from that of the original
  rock.

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Fractional Crystallization

• Fractional crystallization is the process wherein
  different minerals form at different
  temperatures.
• When magma cools, it crystallizes in the reverse
  order of partial meltingthe first minerals to
  crystallize from magma are the last minerals to
  melt during partial melting.

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Bowens Reaction Series

• Bowens reaction series illustrates the
  relationship between cooling magma and mineral
  formation.
• Bowen discovered two main patterns, or branches,
  of crystallization
• The first pattern is characterized by a
  continuous, gradual change of mineral
  compositions in the feldspar group.
• The second pattern is characterized by an abrupt
  change of mineral type in the iron-magnesium
  groups.

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Families of Igneous Rx

• Felsic- rx that are silica rich, are light in
  color (mainly quartz and orthoclase feldspar) can
  be coarse or fine grained
• Granite and obsidian (volcanic glass)
• Intermediate- rx that range in color from dark to
  light containing both felsic and mafic forming
  minerals (a mix of these types of rx) contain
  less quartz than felsic rx
• Diorites and Andesites are common forms
• Mafic- iron and magnesium rich rx that are low in
  silica tend to be dark in color and are mainly
  composed of feldspars and pyroxene minerals and
  lack quartz can be ferromagnetic
• Coarse and fine grain basalts are common forms

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gabbro
pegmatite
granite
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Granite Mineral Composition
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extrusive igneous rocks

• Forms from the cooling of LAVA (magma that has
  reached earths surface)

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Lava flows forming extrusive igneous rocks
(obsidian)
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• Cools QUICKLY (exposed to colder air)
• Rock crystals are SMALL and rocks have a
  fine/glassy texture

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Shiprock, NM An intrusive igneous rock formation
called a volcanic neck
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Pumice is an Extrusive Igneous Rock that is
VESICULAR (has gas pockets). Because pumice
formed so quickly, the rock formed around the
pockets of gas, creating holes in the rock.
This allows the rock to float in water because of
its lower density!
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Key idea

• The texture of the igneous rock is determined by
  the size, shape, and arrangement of the mineral
  crystals!

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types of magma

• FELSIC MAGMA
• Light colored
• Thick (high viscosity)
• Contains high amounts of silica
• Granite

• MAFIC MAGMA
• Dark colored
• Thin (low viscosity)
• Contains high amount of magnesium iron
• Basalt

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the bells whistles for identifying an IGNEOUS
rock

• Igneous rocks have obvious CRYSTALS!!!
• So if you see minerals, its probably igneous!

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sedimentary rocks
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Thought Question

• What are some features/objects you might find in
  a sedimentary rock that you wouldnt find in an
  igneous rock?
• Name and describe one natural process that
  demonstrate weathering and/or erosion.
• Explain where you would expect to find rocks that
  have been metamorphosed.

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Objectives

• Identify the correct sequence of the formation of
  sedimentary rocks
• Name the three main types of sedimentary rocks
  and describe several identifiable sedimentary
  rock features
• Describe clastic sedimentary rocks
• Explain how chemical sedimentary rocks form
• Describe organic sedimentary rocks
• Compare and contrast the different types and
  causes of metamorphic rocks
• Distinguish between regional and contact
  metamorphism
• Explain the difference between metamorphic rock
  features
• Identify foliated and non foliated rocks and give
  examples of each

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Formation of Sediment

• Sediments are pieces of solid material that have
  been deposited on Earths surface by wind, water,
  ice, gravity, or chemical precipitation.
• When sediments become cemented together, they
  form sedimentary rocks.
• The formation of sedimentary rocks begins when
  weathering and erosion produce sediments.
• Chemical dissolving rocks
• Physical breaking into smaller pieces

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Erosion

• Erosion is the removal and movement of surface
  materials from one location to another.
• The four main agents of erosion are wind, moving
  water, gravity, and glaciers.
• Deposition occurs when sediments are laid down on
  the ground or sink to the bottoms of bodies of
  water.
• Sediments are deposited when transport stops.
• As water or wind slows down, the largest
  particles settle out first, then the
  next-largest, and so on, so that different-sized
  particles are sorted into layers.

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Burial

• Most sediments are ultimately deposited on Earth
  in depressions called sedimentary basins where
  they are layered and buried.
• Lithification includes the physical and chemical
  processes that transform sediments into
  sedimentary rocks.
• As more and more sediment is deposited in an
  area, the bottom layers are subjected to
  increasing pressure and temperature which causes
  lithification.

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Lithification

• There are two common types of cementation.

• A new mineral, such as calcite (CaCO3) or iron
  oxide (Fe2O3) grows between sediment grains as
  dissolved minerals precipitate out of groundwater.

• Existing mineral grains grow larger as more of
  the same mineral precipitates from groundwater
  and crystallizes around them.

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Sedimentary Rx- Three Classes

• Clastic- Sedimentary rx made up of rock
  fragments carried by water, wind or ice from
  original source to a new area becomes compacted
  or cemented into solid rx
• Chemical- Sedimentary rx when dissolved minerals
  in water fall out of solution (precipitate out)
  solute is usually water
• Organic- Sedimentary rx that form from the
  remains of once living organisms

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Clastic Sediments

• Conglomerates- sed rx composed of rounded gravel,
  cobbles or pebble fragments that are cemented
  together by water flowing between the cobbles
• Breccias-conglomerates created when angular rx
  are cemented together during a mud flow
• Sandstones- sed rx composed of sand sized grains
  that are cemented together typically made up of
  quartz sands
• Shale- sed rx composed of clay sized particles
  that have been cemented and compacted together
  under pressure into flat layers

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Examples of Clastic Sediments
Breccia
Conglomerate
Sandstone
Shale
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Chemical and Organic Sediments

• Evaporites- dissolved minerals left behind to
  form rocks some minerals dissolve in water and
  reform to create rocks
• Gypsum and Halite (salt flats)
• Coal- made of mostly hydrocarbons from the
  burial, heating and compaction of organic
  material
• Limestone-forms from the collection and
  compaction of the shells of marine organisms
  (corals, clams, plankton, etc.)
• Aragonite is the main component
• Fossils-the remains or traces of plants and
  animals typically preserved in sed rx. often
  only the impressions are left

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Sedimentary Rock Features

• Stratification- the layering of sed rxs whenever
  there is a change in the type of sed being
  deposited or when change in deposit direction or
  the amount of time of layering
• Bedding, or horizontal layering, is the primary
  feature of sedimentary rocks.
• Cross bedding typically from wind blown
  deposits creates feather-like patterns
• Graded-bedding occurs when grain size varies
  during deposition

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Examples of Sedimentary Features
Cross bedding
Graded bedding
Fossil Fish
Fossil Plant Impressions
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More Sedimentary Features

• Ripple marks- wave-like features created by the
  action of moving water or wind on sand
• Mud Cracks- the fossilization of mud after it has
  dried and shrunk, creating cracks found at
  rivers, flood plains, or dry lake beds
• Concretions- areas in sedimentary layers where
  minerals have precipitated from solution around
  an existing rock particle these tend to be
  different than the rock around them

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Sedimentary Rock Features
Stratification
Ripple marks
Mud Cracks
Concretion
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Formation

• Sedimentary rocks form from the COMPACTION
  CEMENTATION of rock fragments
• Rock fragments are glued together by a matrix
  of calcite, silica, or iron oxide

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3 types of sedimentary rocks

• CLASTIC formed from fragments of other rocks
• Sandstone, Conglomerate
• CHEMICAL formed from the mineral precipitates
  of evaporated seawater
• Rock Salt
• ORGANIC formed from the remains of plants
  animals with rock fragments
• Coal, Fossil Limestone

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CLASTIC

• Formed when rock fragments sediment are carried
  deposited by WIND, GLACIERS, RUNNING WATER
• Sediments are DEPOSITED, then COMPACTED finally
  CEMENTED together

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• Fragments that make up these rocks come in many
  shapes sizes
• They are formed from PRE-EXISTING rock that has
  been eroded!!!
• Can be igneous, sedimentary, or metamorphic
  fragments

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Most sediment is carried byRunning Water!

• The further water carries the sediment, the more
  ROUND SMOOTH the particle becomes
• When a stream slows down, it drops the LARGEST
  particles first, the SMALLEST last (HORIZONTAL
  SORTING)

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Conglomerate large sediments that are rounded
(have been transported by a stream!)
Breccia very large sediments that are angular
(note hammer for size reference)
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STRATIFICATION

• Sandstones Siltstones form from smaller
  sediments that tend to create layers of
  sediments in rocks
• This is known as STRATIFICATION (layering)
• There will be layers of SIMILAR colored minerals

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Angels Landing, Zion Natl Park, Utah note
rock layers
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Red Sandstone, Utah note distinct LAYERING of
sediments (sand)
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Horseshoe Bend, Utah
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Grand Canyon Natl Park, Arizona sedimentary
rock formation at its best! The canyons were
formed by the Colorado River cutting into the
rock layers over time!
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CHEMICAL

• Formed when dissolved minerals in seawater are
  deposited (seawater evaporates, leaving the
  minerals behind)
• Usually old swamps, seas, or lakes evaporate
• Also known as CRYSTALLINE because of the fine
  crystals
• Limestone, Rock Salt, Rock Gypsum (sheetrock)

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Salt Mines - Rock Salt is being formed as the
salt water evaporates from the sea.
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Devils Golf Course millions of years ago
this was a sea of salt water. It has been
evaporating over time
and has formed pockets of chemical limestone,
rock salt, and rock gypsum!
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ORGANIC

• Formed from the remains of plants animals that
  are compacted
• Fossil Limestone formed when shell remains of
  marine organisms are cemented in fragments
• Shells are made of CALCITE which reacts with acid
  and is a natural cement

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Brachiopod fossils in limestone
Imprint of a leaf
Trilobite fossils over 250 MILLION years old!!!
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If peat at the bottom of a swamp is buried
compressed, coal may form
Coal note distinct layering of peat
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bells whistles for sedimentary rock
identification!

• Stratification layering of sediments
• Fossils actual remains or imprints
• Ripple marks, mud cracks, etc

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Ripple Marks in the Shale from running water as
the rock was forming!
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ESRT page 7
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metamorphic rocks

• ESRT page 7

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Key ideas

• Formed when existing rocks are changed by HEAT
  PRESSURE
• The new rocks resemble the parent rock
• IMPORTANT- THE ORIGINAL ROCK CANNOT MELT WHEN IT
  BECOMES METAMORPHIC! (If it melts, its igneous!)

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Causes of Metamorphism

• Metamorphic rock forms when high temperature and
  pressure combine to alter the texture,
  mineralogy, or chemical composition of a rock
  without melting it.
• The high temperatures ultimately are derived from
  Earths internal heat.
• The high pressures can be generated in two ways
• From vertical pressure caused by the weight of
  overlying rock
• From the compressive forces generated as rocks
  are deformed during mountain building

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Metamorphism Three Ways

• Contact Metamorphism- occurs when moving magma,
  lava or hot liquid comes into contact with rock
  and only changes rocks near or actually touching
  the hot material
• Regional Metamorphism- metamorphism that occurs
  over a large area (1000km2) due to the movement
  of tectonic plates past one another
• Hydrothermal metamorphism occurs when very hot
  water reacts with rock and alters its chemistry
  and mineralogy.

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Contact Metamorphism
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Contact Metamorphism

• High temperature and moderate-to-low pressure
  form the mineral assemblages that are
  characteristic of contactmetamorphism
• Because temperature decreases with distance from
  an intrusion, metamorphic effects also decrease
  with distance.

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Two Types of Metamorphics

• Nonfoliated- meta rx that do not have definite
  layers or bands often have a coarse grained
  texture
• Marble- metamorphosed limestone
• Quartzite- metamorphosed sandstone

• Foliated-meta rx that have bands of minerals that
  are parallel to one another
• Slates-metamorphosed shale
• Schist-metamorphosed slate
• Gneiss- light and dark bands of crystals

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Examples of Metamorphic Rx
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Metamorphic Textures

• Porphyroblasts

• Under certain conditions, new metamorphic
  minerals can grow quite large while the
  surrounding minerals remain small.
• Porphyroblasts are large crystals, which can
  range in size from a few millimeters to a few
  centimeters.

• Porphyroblasts are found in areas of both contact
  and regional metamorphism.

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Types of metamorphism

• REGIONAL
• Large areas of rock are changed by HEAT PRESSURE

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• CONTACT
• Magma touches layers of rock and the HEAT causes
  the rock layers to change

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Identifying characteristics

• FOLIATION mineral alignment the minerals in
  the rock are layered, which facilitates breakage
  along flat planes
• BANDING alternating layers of different colored
  minerals
• These bands are usually distorted from the heat
  pressure

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More foliation slate phyllite
Foliation note the scratches in the rock
this is mineral alignment!
Excellent example of banding distortion this
is GNEISS ?
Banding mica schist
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Metamorphic mountains formed from regional
metamorphism
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Alaskas Copper Mountain contact metamorphism
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the bells whistles for metamorphic rock
identification

• FOLIATION mineral alignment look for
  scratches in the rocks
• BANDING layers of DIFFERENT COLORS not to be
  confused with sedimentary layers!!!!!! (these
  will be obviously different parent rock layers)

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Okay

• Lets sum up!

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There are 3 classifications of ROCKS

• Igneous formed by the cooling of magma (melted
  rock)
• Sedimentary formed by compaction cementation
  of rock fragments
• Metamorphic formed by heat pressure changing
  existing rocks

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• The ROCK CYCLE shows how each type of rock forms
  how each rock can change into a different type
  of rock!

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The ROCK CYCLE is also found in your ESRT page 6!
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Remember the bells whistles when identifying
rocks!

• Igneous obvious crystals of different minerals
• Sedimentary stratification, fragments, fossils
• Metamorphic foliation, banding

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REVIEW-Major Rock Groups

• Igneous
• Formed from a melt (molten rock)
• Plutonic (intrusive)slow cooling and
  crystallization
• Volcanic (extrusion) quick cooling at the
  surface
• Sedimentary
• Formed at the Earths surface
• Clastic (Mineral Fragments or grains, clays)
• Chemical (crystalline chemical/biochemical
  precipitates)
• Metamorphic
• Changed by pressure, temperature and fluids.

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Fig. 2.9
MAGMA
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IGNEOUS
Crystallization
MAGMA
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IGNEOUS Plutonic
Crystallization
MAGMA
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Volcanic IGNEOUS Plutonic
Crystallization
MAGMA
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Weathering
Volcanic IGNEOUS Plutonic
Crystallization
MAGMA
Uplift
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SEDIMENT
SEDIMENT
Weathering
Volcanic IGNEOUS Plutonic
Crystallization
MAGMA
Uplift
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Erosion
SEDIMENT
Weathering
Transport
Deposition
Volcanic IGNEOUS Plutonic
SEDIMENTARY
Crystallization
MAGMA
Uplift
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Erosion
SEDIMENT
Weathering
Transport
Deposition
Volcanic IGNEOUS Plutonic
SEDIMENTARY
Crystallization
MAGMA
Uplift
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Erosion
SEDIMENT
Weathering
Transport
Deposition
Volcanic IGNEOUS Plutonic
SEDIMENTARY
Increased PT
METAMORPHIC
Crystallization
Burial
MAGMA
Uplift
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Erosion
SEDIMENT
Weathering
Transport
Deposition
Volcanic IGNEOUS Plutonic
Can you see any shortcuts?
SEDIMENTARY
Increased PT
METAMORPHIC
Crystallization
Melting
Burial
MAGMA
Uplift
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Erosion
SEDIMENT
Weathering
Transport
Deposition
Volcanic IGNEOUS Plutonic
SEDIMENTARY
Increased PT
METAMORPHIC
Crystallization
Melting
Burial
MAGMA
Uplift
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In Conclusion

• The rock cycle demonstrates the relationships
  among the three major rock groups
• It is powered by the interior heat of the Earth
• As well as earths momentum and
• The energy from the sun
• It involves processes on the Earths surface as
  well as the Earths interior
• It connects the hydrologic cycle with the
  tectonic cycle.

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Erosion
SEDIMENT
Weathering
Transport
Deposition
Volcanic IGNEOUS Plutonic
SEDIMENTARY
Increased PT
METAMORPHIC
Crystallization
Melting
Burial
MAGMA
Uplift