Rocks:Ig

neou

s

Igne

ous Se

dim

enta

ry

Sedi

men

tary

Metamorp

hic

Metamorp

hic

Keepers of Earth’s HistoryKeepers of Earth’s History 1

What’s in your rock?:

Hornblende

Orthoclase

Quartz

aggregates of minerals

Granite

Biological material

Fossil fragments

Plant material

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Understanding rocks is the basic foundation ofknowledge for earth scientists and materials thatmake up the earth.

Understanding rocks is the basic foundation ofknowledge for earth scientists and materials thatmake up the earth.

• Every rock “speaks” to the observer and gives clues about where and how it was formed.• Rocks are divided into 3 major groups:

• Igneous• formed from solidifying hot molten

rock (magma)

• Every rock “speaks” to the observer and gives clues about where and how it was formed.• Rocks are divided into 3 major groups:

• Igneous• formed from solidifying hot molten

rock (magma)• Sedimentary

• formed on the surface of the earth from weathering processes

• Sedimentary• formed on the surface of the earth from

weathering processes

• Metamorphic• pre-existing rocks are subjected to

various pressure and temperature relationships

• Metamorphic• pre-existing rocks are subjected to

various pressure and temperature relationships

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How does an earth scientist distinguish betweenthe three rock types (Ig, Seed, and Met)?

Texture:• the appearance of the rock

• size, shape, and arrangement of mineral grains.

Composition (mineral assemblages)• types and relative proportions of minerals

making up a rock

• composition, mineral make-up, chemistry--all indicators of a rock’s composition

All rocks are identified based on their texture and composition. 5

The Rock CycleThe Rock Cycle

The Sedimentary CycleThe Sedimentary Cycle

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The Rock Cycle:• where the earth’s internal forces meet the earth’s external forces (at the earth’s surface)

Earth’s internal forces Earth’s external forces

• moving continents (PT)• earthquakes• elevation of mountains• volcanic eruptions

• the hydrosphere (HC)• atmosphere• erosion (wind, water, ice)• biosphere activities

Produce a continuous cycle of rising mountains only to beweathered down and uplifted repeatedly. As a result, igneoussedimentary, and metamorphic rocks are created.

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I I Earth Science, especiallythe rock cycle !!!!!!!!!!!!! Earth Science, especiallythe rock cycle !!!!!!!!!!!!!

I will get an A on my exams and quizzes.

Discuss with a friend:

1.Briefly identify each rock group and its geologic environment.

2. Draw the rock cycle, and explain how the rock cycle works to your neighbor.

3. Why is the rock cycle a “cycle”???

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Geology – Chapter 3 – Igneous Rocks

Igneous RocksIgneous Rocks

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MagmaMagma

Extrusive - igneous rocks – above the earth’s surface volcanic rocks lava flows Example – Hawaiian Volcanoes

Intrusive - igneous rocks – below the earth’s surfaceplutonic rockslarge granite mountainsExample – Sierra Nevada Mountain Range

• the parent material for igneous rocks (if not all rock groups)

• typical temperature 1,200oC (2,200oF)• forms about 250 km or 150 miles below the earth’s surface

Grain size determines if the ig rock is extrusive orintrusive. Magma determines the rock’s composition.

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When observing “frozen magma” (an igneous rock), how does a geologist know if the rock is an Extrusive orIntrusive igneous rock?

When observing “frozen magma” (an igneous rock), how does a geologist know if the rock is an Extrusive orIntrusive igneous rock?

checking the crystal size - Does the rock contain visible crystals, or are crystals non-existent?checking the crystal size - Does the rock contain visible crystals, or are crystals non-existent?

Factors that affect crystal size in an igneous rock:The rate at which magma cools

• slow cooling – visible minerals• rapid cooling – non-visible minerals

Factors that affect crystal size in an igneous rock:The rate at which magma cools

• slow cooling – visible minerals• rapid cooling – non-visible minerals

Igneous Rock TexturesIgneous Rock Textures

• non-visible minerals• rapid cooling magma• extrusive ig rock

• non-visible minerals• rapid cooling magma• extrusive ig rock

• visible minerals• slow cooling magma• intrusive ig rock

• visible minerals• slow cooling magma• intrusive ig rock

Cooled above thesurface (fine-grained)

Cooled above thesurface (fine-grained)

Cooled below the surface (coarse-grained)

Cooled below the surface (coarse-grained) 11

Composition of Igneous RocksHow much silica (SiO2) is in your igneous rock?Felsic compositions (feldspar + silica)

• light-colored igneous rocks• common minerals: feldspar and quartz• 70% SiO2

Mafic compositions (magnesium + iron)• dark-colored igneous rocks• common minerals: olivine and pyroxene• 50% SiO2

• ultramafic: composed entirely of olivine and pyroxene and less than 50% silica (SiO2)

Intermediate compositions:• mixture of felsic and mafic minerals• about 60% silica (SiO2)

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How are igneous rocks classified?• Using their TEXTURE and COMPOSITION

Igneous rocks are classified based on TEXTURE andCOMPOSITION.

TE

XT

UR

E

CO

AR

SE

ph

aneritic

FIN

Eap

han

itic

COMPOSITIONFelsic (light color)

70% silicaMafic (dark color)

50% silicaIntermediate color

60% silica

Granite Diorite Gabbro

Rhyolite Andesite Basalt

Igneous rocks have the same chemistry but different textural characteristics due to the type of geologic environment (cools quickly or slowly).

I I Earth Science, especiallyigneous rocks. Earth Science, especiallyigneous rocks.

I will get an A on my exams and quizzes.

1.What is the difference between extrusive and intrusive igneous rocks?2. How can one tell the difference between an extrusive and intrusive rock texture?3. The composition of a mafic ig rock is…. The composition of a felsic ig rock is ….4. A fine-grained, light-colored ig rock is called a ………………….

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Sedimentary RocksSedimentary Rocks

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How is a sedimentary rock formed???How is a sedimentary rock formed???

Pre-existingRock

Pre-existingRock

erosionerosion

water, wind, ice

water, wind, ice

breaks downpre-existing rockbreaks downpre-existing rock

sedimentsediment

transportedtransportedLakesLakes

RiversRivers

Depos

ited

Depos

ited

compactedcemented

compactedcemented

lithifiedlithified SedimentaryRock

SedimentaryRock

Why is the earth’s surface 75% sedimentary rocks?Why is the earth’s surface 75% sedimentary rocks?19

Erosional processes – later (Chapter 4)Erosional processes – later (Chapter 4)

Sediments are separated into 3 broad categories:

• Clastic sediments: inorganic grains or mineral fragments ranging in size from boulders to clay particles (flour size)

• Chemical sediment: formed by the precipitation of minerals dissolved in lakes, rivers, or seawater environments

• Biogenic (bioclastic) sediment: sediment composed of animal and plant remains or material precipitated by biological processes

Sediments are separated into 3 broad categories:

• Clastic sediments: inorganic grains or mineral fragments ranging in size from boulders to clay particles (flour size)

• Chemical sediment: formed by the precipitation of minerals dissolved in lakes, rivers, or seawater environments

• Biogenic (bioclastic) sediment: sediment composed of animal and plant remains or material precipitated by biological processes To be a sedimentary rock, it must be lithified.To be a sedimentary rock, it must be lithified.

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Lithification: processes by which sediment is transformed into sedimentary rockLithification: processes by which sediment is transformed into sedimentary rock

Sediment can be lithified in three common processes: Sediment can be lithified in three common processes: Compaction: Overlying weight of the sediment “squeezes”and compresses pore spaces, which pushes particles together.Compaction: Overlying weight of the sediment “squeezes”and compresses pore spaces, which pushes particles together.

A B

A. loose, unconsolidated sediment with abundant pore spaceB. compacted, compressed sediment with reduced pore space

A. loose, unconsolidated sediment with abundant pore spaceB. compacted, compressed sediment with reduced pore space

Cementation: Pore water is expelled from voids, and risingwater carries iron, calcium carbonate, and silica which precipitates as geological glue (cement) holding the grains together.

Cementation: Pore water is expelled from voids, and risingwater carries iron, calcium carbonate, and silica which precipitates as geological glue (cement) holding the grains together.

Grains are cemented together by three types of cements:

• iron cement• calcium carbonate cement• silica cement

Grains are cemented together by three types of cements:

• iron cement• calcium carbonate cement• silica cement 22

Lithification processes

Recrystallization: Overlying pressure causes less stableminerals to convert to more stable minerals, producing new substances that cement pre-existing grains.

Recrystallization: Overlying pressure causes less stableminerals to convert to more stable minerals, producing new substances that cement pre-existing grains.

Overlying pressureOverlying pressure Grain boundaries convertto more stable mineral

compositions, “cementing”grains together.

Grain boundaries convertto more stable mineral

compositions, “cementing”grains together.

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Clastic Sediment:Clastic Sediment:

lithifiedlithifiedgravel sediment rangingfrom pea-sized to largergravel sediment rangingfrom pea-sized to larger conglomerateconglomerate

sand-sized particles (fine to coarsesandpaper)

sand-sized particles (fine to coarsesandpaper)

sandstonesandstone

finer particles – size of table saltfiner particles – size of table saltsiltstonesiltstone

finest sedimentaryparticles (flour-size)finest sedimentaryparticles (flour-size) shaleshale

lithifiedlithified

lithifiedlithified

lithifiedlithified

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Chemical Sediments and Sedimentary Rocks

Chemical Sediment: sediment formed by the precipitationof minerals dissolved in a lake, river, or seawaterChemical Sediment: sediment formed by the precipitationof minerals dissolved in a lake, river, or seawater

All surface water and groundwater contain dissolved ions (chemicals), creating a venue for precipitation of chemical sediment.

All surface water and groundwater contain dissolved ions (chemicals), creating a venue for precipitation of chemical sediment.

Precipitation of chemical rocks takes place in two ways:

• Plants and animals alter the chemical balance of the water body (lake, ocean).

Increasing amounts of calcium carbonate cause precipitation of limestone.

• evaporation of chemically saturated water bodies

Precipitation of chemical rocks takes place in two ways:

• Plants and animals alter the chemical balance of the water body (lake, ocean).

Increasing amounts of calcium carbonate cause precipitation of limestone.

• evaporation of chemically saturated water bodies 26

Evaporation of chemically saturated water createsa chemical sedimentary rock (evaporite).

Na+Na+ Na+Na+

Na+Na+ Na+Na+

Cl-Cl-

Cl-Cl-

Cl-Cl-Cl-Cl- a lake containing sodium (Na+)

and chlorine (Cl-)--free ionsa lake containing sodium (Na+)and chlorine (Cl-)--free ions

EvaporationEvaporation

NaCl

Lake water is evaporated,concentrating sodium andchloride ions (saturation).

Sodium and chlorine combineto form halite (table salt).

Lake water is evaporated,concentrating sodium andchloride ions (saturation).

Sodium and chlorine combineto form halite (table salt).

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The Great Salt Lake, Utah(evaporite halite)

The Great Salt Lake, Utah(evaporite halite)

UtahUtah

As lake becomes saturated,density of water increases.As lake becomes saturated,density of water increases.

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Chemical – sedimentary rocks that have beenprecipitated or are the result of evaporation Chemical – sedimentary rocks that have beenprecipitated or are the result of evaporation

Gypsum – evaporite CaSO4Gypsum – evaporite CaSO4

Halite – evaporiteNaCl

Halite – evaporiteNaCl

Limestone--precipitated

calcium carbonate

Limestone--precipitated

calcium carbonate

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Biogenic Sediments and Biogenic Rocks:Biogenic sediment is composed of organic remains of plants andanimals (bioclastic rocks).

• shell, bones, teeth, plant fragments, wood, roots

Biogenic Sediments and Biogenic Rocks:Biogenic sediment is composed of organic remains of plants andanimals (bioclastic rocks).

• shell, bones, teeth, plant fragments, wood, roots

Common Biogenic Rocks:• Limestone

• most abundant biogenic sedimentary rock• composed of calcium carbonate CaCO3(calcite, dolostone,

aragonite)• lithified shells, skeletal material

Common Biogenic Rocks:• Limestone

• most abundant biogenic sedimentary rock• composed of calcium carbonate CaCO3(calcite, dolostone,

aragonite)• lithified shells, skeletal material

• Chert• composed of silica SiO2

• precipitated silica shells (made by sea animals) that protect microscopic sea animals – Animals die, and silica shells sink, creating layers of chert beds on the ocean floor.

• Chert• composed of silica SiO2

• precipitated silica shells (made by sea animals) that protect microscopic sea animals – Animals die, and silica shells sink, creating layers of chert beds on the ocean floor.

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“When the animal dies, it loses the chert off its back.”“When the animal dies, it loses the chert off its back.”

Common Biogenic RocksCommon Biogenic Rocks

Peat to Coal• accumulated remains of terrestrial plants• with time and pressure ---- peat• continued pressure and lithification ------ coal

Peat to Coal• accumulated remains of terrestrial plants• with time and pressure ---- peat• continued pressure and lithification ------ coal

PeatPeat

Bituminous coalBituminous coal

Anthracite coalAnthracite coal

Increasing pressure

Increasing pressuremetamorphismmetamorphism

lithificationlithification

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Biogenic (bio-clastic) rocks –

result from animal and plant secretions -- The term “clastic” indicates that these rocks contain fossils or parts of plants, shells, compacted plant material

Biogenic (bio-clastic) rocks –

result from animal and plant secretions -- The term “clastic” indicates that these rocks contain fossils or parts of plants, shells, compacted plant material

Animal partsAnimal parts

Cemented shell fragmentsCemented shell fragments

CoquinaCoquina

Fossil LimestoneFossil Limestone

Chalk

Microscopic fossils

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What do sedimentary rocks tell the earthscientist?What do sedimentary rocks tell the earthscientist?

These rock “layers” weredeposited one layer at a time and lithified.

The banded appearanceis known as bedding orgroups of layers called strata.

The boundary between each stratum is called a bedding surface.

These rock “layers” weredeposited one layer at a time and lithified.

The banded appearanceis known as bedding orgroups of layers called strata.

The boundary between each stratum is called a bedding surface.

stratastratabeddingbedding

Bedding surface

By observing the sedimentary rock type (clastic, chemical,biogenic) and depositional patterns, an earth scientist candecipher the geologic history – like reading pages in a book.

By observing the sedimentary rock type (clastic, chemical,biogenic) and depositional patterns, an earth scientist candecipher the geologic history – like reading pages in a book.33

Sedimentary Rock Classification Summary TreeSedimentary Rocks are divided into 3-classification categories:

Clastic sediments Chemical sediments Bio-clastic (chemical)sediments

composed of inorganicgrains

formed by precipitation

plants andanimals

evaporationprocesses

composed of “animal parts”from

classification based on distribution of grain sizes

Conglomerate

Sandstone

Shale

Siltstone

Decreasing grain size

Classification based onlack of grains and chemical

composition

Gypsum (CaSO4)

Halite (NaCl)

Limestone (CaCO3)

Classification based onObserved fossils, animal parts,

Plant/animal secretions

Fossil-limestone

Coquina

Chalk

I I sedimentary rock classification. sedimentary rock classification.

I will get an A on my exams and quizzes.

Discuss with a friend:

1.Describe at least 2 characteristics of each sedimentary rock classification (clastic, biogenic, chemical).

2.Give a rock example for each classification.

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What is “metamorphism?” What is “metamorphism?”

• transformation of pre-existing rock to a metamorphic rock through pressure and temperature relationships

• transformation of pre-existing rock to a metamorphic rock through pressure and temperature relationships

• meta (change) morphism (form)• meta (change) morphism (form)

• All changes take place through solid state transformation.

• All changes take place through solid state transformation.

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Types of Metamorphism• takes place around 150oC (Temperature) • typically at depths of 5 km below the earth’s surface (Pressure)

Types of Metamorphism• takes place around 150oC (Temperature) • typically at depths of 5 km below the earth’s surface (Pressure)

At this temperature and pressure, new mineralsare formed – changed from one mineral to another.

At this temperature and pressure, new mineralsare formed – changed from one mineral to another.

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I I metamorphic rocks. metamorphic rocks.

I will get an A on my exams and quizzes.

Discuss with a friend:

1.How do you define metamorphism? – Be specific.

2.What two major factors are necessary for pre-existing rocks to become metamorphosed?3. Where does metamorphism typically take place within the earth?

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2 Common types of metamorphism2 Common types of metamorphism

• contact metamorphism

• regional metamorphism

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What is contact metamorphism?What is contact metamorphism?

• Contact metamorphism:

magma “contacts” solid rock – heat is transferred into overlying

rocks through conduction – changing the pre-existing rock it intruded

• high heat/low pressure• localized metamorphism• “fast-acting,” like touching a

hot frying pan

• Contact metamorphism:

magma “contacts” solid rock – heat is transferred into overlying

rocks through conduction – changing the pre-existing rock it intruded

• high heat/low pressure• localized metamorphism• “fast-acting,” like touching a

hot frying pan 45

Country rock (surrounding) is baked from conduction.

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What is regional metamorphism?What is regional metamorphism?

Regional Metamorphism

Pre-existing rock is subjected to intensestresses and strains (deformation) usuallyfrom the forces of mountain building.

• high heat/high pressure• very widespread geographically• like experiencing a slow sunburn

Regional Metamorphism

Pre-existing rock is subjected to intensestresses and strains (deformation) usuallyfrom the forces of mountain building.

• high heat/high pressure• very widespread geographically• like experiencing a slow sunburn

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Mountain building

widespread belts

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I I the different ways to createMetamorphism. the different ways to createMetamorphism.

I will get an A on my exams and quizzes.

Discuss with a friend:

Describe the conditions necessary for eachtype of metamorphism:

• contact metamorphism• regional metamorphism

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Heat sources:contact with hot magma – heat penetrates

overlying rocks (conduction)

geothermal gradient – heat increases with depth – rocks are hotter when buried

Heat sources:contact with hot magma – heat penetrates

overlying rocks (conduction)

geothermal gradient – heat increases with depth – rocks are hotter when buried

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Metamorphic heat sources:

Geothermal Gradient

• Temperature increases as depth increases.

• Large thermal gradient is at the surface.

• Gradient decreases after 1000 km depth.

Geothermal Gradient

• Temperature increases as depth increases.

• Large thermal gradient is at the surface.

• Gradient decreases after 1000 km depth.

10001000 20002000 30003000 4000400000

Steep gradientSteep gradient

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Pressure – increases with depth,various types of pressure rearrangeminerals – minerals compact or elongate

Pressure – increases with depth,various types of pressure rearrangeminerals – minerals compact or elongate

Confining pressure Differential pressure

52Pressure associated with metamorphism

How does one know how much metamorphismhas taken place in a rock?• reflected in the rock’s texture

How does one know how much metamorphismhas taken place in a rock?• reflected in the rock’s texture

Not MetamorphosedNot Metamorphosed

Metamorphosed – mineralgrains are in a preferred direction -- FOLIATION

Metamorphosed – mineralgrains are in a preferred direction -- FOLIATION

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I I to metamorphose. to metamorphose.

I will get an A on my exams and quizzes.

Discuss with a friend:

1.Describe two heat sources associated with metamorphism.2.Define the differences between confining and differential pressures.3. Draw a diagram that shows mineral orientation due to confining and differential type pressures.

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