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Objectives
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Identify major types of rock, explain how they form
Summarize steps in the rock cycle
Summarize the factors that affect stability of rocks
Summarize factors that affect whether rock melts
Describe how cooling rate of magma and lava affects
texture of igneous rocks
 Classify igneous rocks according to composition and
texture
 Describe intrusive and extrusive igneous rock structures
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Explain processes of compaction and cementation
Describe how chemical and organic sedimentary
rocks form
Describe how clastic sedimentary rock forms
Identify the sedimentary rock features
Describe the process of metamorphism
Explain the difference between regional and contact
metamorphism
Distinguish between foliated and nonfoliated
metamorphic rocks, give example of each
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What defines a rock?
 Material that makes up solid parts of Earth, 1 or
more minerals, or made of solid organic matter
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Types
 Igneous rock- forms from magma
▪ Means from fire
 Sedimentary-forms from sediment that is
compressed and cemented together. How?
 Metamorphic-forms when existing rock is altered.
How?
▪ Means changed from
Rock cycle-series of processes in which rock forms,
changes from one type to another, destroyed and
forms again by geological processes
 Steps
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 Igneous is exposed and broken into sediment
 Sediment is compacted and cemented
 Sedimentary rock becomes metamorphic through certain
changes
 Metamorphic rock melts and forms magma
 New igneous rock
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Factors that affect stability
 Chemical Stability
▪ Chemical compound maintains stability or breaks down
to form different chemical
▪ Depends on chemical bonds between atoms in mineral
▪ More bonds between silicon and oxygen=more resistant
 Physical Stability
▪ Rocks have natural zones of weakness, determined
where rocks form
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What are igneous rocks?
 Rocks that form when magma cools and solidifies.
Most are made of crystals
 How does magma form?
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What are the factors that affect whether a
rock melts?
 Temperature, pressure, presence of fluid in rock
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Partial melting
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Intrusive igneous-rock formed from cooling
and solidification of magma beneath Earth’s
surface
Extrusive igneous-rock that forms from the
cooling and solidification of lava at Earth’s
surface
 Differ in size of crystals or grains
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Texture determined by size of crystals in
rock-size determined by cooling rate
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Coarse grained-large mineral grains
 Ex. Granite
 Slow loss of heat=large crystals
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Fined grained-small crystals
 Ex. Basalt and rhyolite
 Cools rapidly
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Porphyritic-large crystals embedded w/ small
 Cools slowly then more rapidly near surface
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Glassy-few crystals
 Ex. Obsidian
 Cools quickly, contains small % of dissolved gases
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Vesicular-full of holes
 Ex. Pumice
 Cools rapidly, contains large % of dissolved gases
GRANITE-COARSE
BASALT-FINE
PUMICE-VESICULAR
OBSIDIAN-GLASSY
Composition-determined by chemical composition
of magma
 Divided into 3 families; Felsic, mafic, intermediate
 Felsic Rock
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 Magma contains a lot of silica
 Light coloring
 Contains plagioclase feldspar, biotite mica, muscovite
mica
 Ex. Granite, rhyolite, obsidian, pumice
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M
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Mafic Rock
 Magma has lower proportions of silica
 Rich in iron and magnesium
 Contains plagioclase feldspar, pyroxene minerals. Also
ferromganesian minerals-hornblende
 Ex. Basalt and gabbro
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Intermediate Rock
 Minerals such as plagioclase feldspar, hornblende,
pyroxene, biotite mica
 Lower proportions of silica than felsic, higher than mafic
 Ex. Diorite and andesite
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What is an intrusion?
 Igneous rock masses that form underground
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Types of intrusive rock structures
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Batholiths-forms cores of mt ranges
Stocks-similar to batholiths, smaller
Laccoliths-form small dome shaped mts
Sills-lies parallel to layers of rock around it
Dikes-cut across rock layers. Common in areas of
volcanic activity
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What are extrusions?
 Igneous rock masses that form on Earth’s surface
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Types of extrusions
 Volcano-vent in which magma, gases, volcanic ash are
expelled
▪ Volcanic neck-solidified central vent
▪ Narrow dikes may be exposed
 Lava flows-flat masses of rock
 Lava plateau-series of lava flows that cover vast area w/
thick rock
 Tuff-volcanic ash deposits
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What is sediment?
 Loose fragments of rock, minerals, and organic
material, result of natural processes
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Transported by wind, water or ice
Sediment looses chemical and physical
composition
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Compaction
 Sediment is squeezed, size of pore space between
sediment grains is reduced by weight and
pressure of overlying layers
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Cementation
 Sediments are glued together by minerals that
are deposited by water
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Form from minerals once dissolved in water
Form when dissolved minerals precipitate out
of water because of changing concentrations
of chemical
 Why do minerals precipitate?
▪ Evaporation
 Ex. Gypsum and halite
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Form from remains of living things
 Coal, limestone
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What makes up coal?
What makes up limestone?
Chalk
 Shells of tiny, one celled organism
COAL-ANTHRACITE
LIMESTONE
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Sedimentary rock that forms when fragments
of pre-existing rocks are compacted or
cemented together
Types
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Conglomerate-rounded fragments
Breccia-angular and have sharp corners
Sandstone-sand sized grains cemented
Shale-clay sized particles cemented and
compacted together, easily split apart
BRECCIA
CONGLOMERATE
SANDSTONE
SHALE
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How are sediments transported?
Characteristics of sedimentary rock
 Stratification-layering of rock, occurs when conditions of
sediment deposition changes
▪ Beds=stratified layers
▪ Massive beds=no internal structures
 Cross beds-slanting layers of sed rock form w/in beds
▪ Sand dunes or river beds
 Graded bedding-various sizes and kinds of material in one
layer
▪ Reverse grading=smallest grains on top of large grains
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Ripple Marks-caused by action of wind or water
on sand
 Sandstone
Mud Cracks-form when muddy deposits dry and
shrink
 River’s flood plain, dry lake bed
Fossils-remains or traces of ancient plants and
animals
Concretions-lumps of rock w/ different
composition of main rock body
 Geode=rock that forms when minerals crystallize
inside cavity of sed rock
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What is metamorphism?
 Process in which heat, pressure, or chemical
processes change one type of rock to another
 Forms from existing igneous, sedimentary or
metamorphic rock
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What causes minerals to change into other
minerals?
Types of metamorphism
 Regional and Contact
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Contact Metamorphism
 Change in texture, structure, chemical composition of rock
due to contact w/ magma
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Regional Metamorphism
 Change in texture, structure, or chemical composition of
rock due to changes in temperature and pressure over
large area
 Tectonic forces
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Which way do you believe most metamorphic rock
is formed?
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Classified on texture and chemical composition
Types of Rocks
 Foliated-minerals arranged in planes or bands
▪ Extreme pressure causes crystals to realign or regrow
▪ Minerals w/ different compositions separate-dark and light bands
 Non-foliated-no bands or aligned minerals
▪ Original rock contains grains of only one mineral, or small amounts
of other minerals
▪ Original may contain grains that are round or square
▪ Ex. Quartzite and marble
GNEISS
MARBLE
QUARTZITE
SLATE