ROCK ON_ by linxiaoqin

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									 Chapter 2
  Rocks
Introduction to the world
directly beneath our feet
            Why study rocks?
   Three reasons…

 To find and utilize
  natural resources
 Prepare for and
  maybe prevent
  natural disasters
 Learn about
  earth’s natural
  history
 Natural           Understand            Earth’s
Resources           Disasters            History
   Coal              Earthquakes      All rocks tell
   Petroleum         Volcanoes         an individual
   Gravel            Landslides        story about
   Uranium                              their past
                      Tsunami’s
   All metals                          If we look and
    used in           Sink Holes        listen closely,
    construction      Foundation        we can gain
   Aquifers           Problems          knowledge of
                                         our planet’s
                                         history
        Three basic rock types
 We   classify rocks into three categories

 These categories are distinguished by how
 each rock type is formed

   Igneous     Sedimentary       Metamorphic
     Rocks          Rocks               Rocks
     The Three Rock Types
 Igneous– Rocks Born of Crystallized
 Fiery Molten Magma or Lava

 Sedimentary– Rocks Born of Layered
 Water or Wind Deposits

            – Rocks Born of a
 Metamorphic
 Change Deep Within the Earth
 Magma or Lava….which is it?
 Magma  – hot
 molten rock that is
 beneath the surface
 of the earth

 Lava– hot molten
 rock that has
 reached the surface
 of the earth
How does an Igneous Rock Form?

   Crystallization – the solidifying of magma
    either at depth or on the exposed surface
    of the earth
      To become Sedimentary---
   1. Weathering – rocks
    exposed at the surface
    undergo disintegration
    and decomposition from
    natural forces
   Water, wind, glaciers,
    waves, heat, etc…
   All these forces will
    break down rocks and
    transport the smaller
    broken down pieces
   These broken down
    pieces are now called…
              SEDIMENTS
 Sediments – the eroded particles of
 rock that have been transported
 away from the original rock
   2. Transportation
   3. Lithification (compaction and
    cementation)– literally means
    “conversion into a rock”

   Lithification is when compacted and
    cemented sediments get buried and
    formed into a new rock

   Hence, sedimentary rocksaddition
     More pressure is applied due to the
     of overlying layers
                                         
      Sediment grains are fused and cemented
      together as the water content is reduced
Check out all these sedimentary layers
  Sky Walk
 Two   things can happen to
  sedimentary rocks:
 They either get exposed at the
  surface as sedimentary rocks for us
  to find, or…
 They continue to get buried deeper
  and deeper within the earth’s crust
       To become Metamorphic
 1.   rocks get buried very, very deep

 2.The intense heat and pressure of
 deep burial will ultimately change the
 rocks into something new
         Metamorphosis
 Metamorphic  Rock – a rock that has
 been changed from its original
 parent rock to a new form due to
 intense heat and pressure
And if you want to go even deeper?
 Rocks that reach depths where the
 heat is extreme enough will turn
 back into molten rock material...

 We   have come full circle
   Time, we need more time
 All the processes of the rock cycle
  happen over incredible time spans
 We cannot see the entire cycle in
  action, it takes much too long
 We see the results of different stages
  of the cycle
 Evidence for the cycle is found
  everywhere, in every rock
What Cycle are we Talking about?


 ROCK  CYCLE – The series of geologic
 processes that forms igneous,
 sedimentary, and metamorphic rocks and
 then breaks them down only to form
 new rocks again at a later time and place

 Developed   by James Hutton
THE ROCK CYCLE
ROCK CYCLE with Diagrams
                 To Review:
 There are 3 main           Heat & Pressure form
  reasons to study rocks      metamorphic rocks
 There are 3 rock types:    The Rock Cycle is not
  igneous, sedimentary, &     just a one way street
  metamorphic                There are varying
 Magma & Lava are not        paths, and rocks can
  quite the same thing        reform or skip whole
 Erosion must occur to       sections of the cycle
  form sediments             Geologic processes
 Deposition occurs to        take incredible amounts
  form sedimentary rocks      of time
Lubbock Haboob
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IGNEOUS ROCKS

   Fire Rocks
    Yosemite
          Igneous formations
 PikesPeak in the Rockies--Colorado
 Mount Rushmore, South Dakota

 White Mountains of New Hampshire

 Stone Mountain in Georgia

 Yosemite-- California
           Igneous Rock Facts
 Form from the slow cooling of magma or
  the quick cooling of lava on the surface
 Most abundant rock on earth

 Magma can rise from depths of 200 km or
  more
 This cross section
 of the earth shows
 how magma can
 crystallize under
 the surface or how
 lava can erupt and
 then cool on the
 surface
Aboveground or Underground?
   Igneous rocks can be subdivided into two
    main categories: intrusive or extrusive

   Intrusive – igneous rocks formed inside the
    earth at depth from cooling of magma

   Extrusive – igneous rocks formed on the
    earth’s surface from cooling of lava

   A note about magma: it’s mostly hot
    molten rock, but it does contain some solid
    material and some dissolved gasses
Classifying all the Igneous Rocks
     Two criteria are used when
      classifying igneous rocks:

 TEXTURE – overall appearance of the
 rock based upon the size and
 arrangement of the crystals

 MINERAL   COMPONENTS - Chemistry
                  Textures
 Four   textures used for all igneous rocks

 Coarse-grained    texture (large)

 Fine-grained   texture (small)

 Porphyritic   texture (mixed)

 Glassy   texture (none)
                   Igneous Textures
   Coarse-grained –
    rocks that cool
    slowly at depth and
    crystals are large
    enough to be seen
    with the naked eye

                                                 Granite is a very common
   This texture is                              example of a coarse-
    inherently intrusive                         grained igneous rock



    Rhyolite is the fine grained version of granite – same mineral different cooliing
    history
          Igneous Textures
 Fine-grained – rock
  cools more rapidly on
  or near surface and
  crystals are small
  and can only be seen
  with a microscope.
 This texture is
  inherently extrusive
                          Basaltic lava flows are
Hawaiian Islands and      very common and are
                          good examples of fine-
Iceland composed          grained igneous rocks
primarily of basalt.
             Igneous Textures
   Porphyritic – rock
    that has large
    visible crystals
    embedded in a
    matrix of fine-
    grained crystals

                            Porphyritic rocks usually
   This texture is both    have the appearance of
    intrusive & extrusive   chocolate chip cookies
             Igneous Textures
   Glassy – rocks that
    cool so rapidly that
    crystals do not form

   This Volcanic Glass
    is the result of a
    violent eruption
                           Obsidian is volcanic glass
                           and is the result of rapidly
   This texture is        cooling lava (no crystals)
    inherently extrusive
       The Chemistry of Magma
   Magma has different chemicals in it

   The chemicals determine what minerals will form

   The same magma can actually produce a wide
    variety of minerals and therefore a wide variety
    of different igneous rocks

   N.L. Bowen came up with a way to predict which
    minerals will form in a cooling magma body

   He charted mineral formation in the BOWEN
    REACTION SERIES
 The Sliding Scale of Igneous Rocks
 Granitic         Light-colored    Rich in SiO2      Least Dense
                                  Sparse Fe & Mg
  (Felsic)

Andesitic        Medium-colored
(Intermediate)

 Basaltic         Dark-colored
  (Mafic)

                                  Rich in Fe & Mg
Ultramafic
                   Very-dark      Sparse in SiO2    Highest Density
Chemistry of Magma & Minerals
The Bowen Reaction Series (pg 39)
    How do we know the names?
   Igneous rocks are classified by their
    texture and their chemistry right?

   And Bowen figured out which minerals will
    form when right?

   So we make a chart that correlates all of
    these characteristics

   Then we simply give each rock a name
Igneous Rock Names (pg 41)
                   To Review:
   Igneous Rocks form from      There are 4 textures that
    the cooling of either         you need to know
    magma or lava                The four chemistry types
   Igneous rocks can form        are: granitic, andesitic,
    on the surface or deep        basaltic, & ultramafic
    within the earth –           Know how to read and
    extrusive and intrusive       understand the Bowen’s
   We classify igneous           reaction series
    rocks by two criteria –      Know how to read and
    texture & chemistry           understand an igneous
                                  naming chart
SEDIMENTARY
   ROCKS
Rocks of Wind & Water
    Sedimentary Rock Facts
 Remember,  sediments are broken
 down rock fragments from other
 rocks due to weathering & transport

 Sedimentary   rocks are only 5-10% of
 all rocks in the crust

 But, sed rocks are over 75% of all
 visible land rocks
Sed Rocks are great story tellers
   Sedimentary rocks tell the story of the past

 They show what kind of climate and area
  the rock formed in
 They show what kind of depositional
  environment the rock was formed in
 Ex. dunes, streams, ocean bottoms, salt
  flats, etc…
 And most importantly, they are the only
  rocks that contain fossils
       Two types of Sed Rocks

         DETRITAL                 CHEMICAL

   Sed rocks that           Sed rocks that
    form from the solid       form from material
    weathered particles       that precipitates
    of other existing         out of an aqueous
    rocks                     solution
            DETRITAL ROCKS
   All minerals can be weathered down into
    sediments and transported

   Therefore you will find all types of minerals in
    sedimentary rocks

   However, quartz & clay minerals are predominant


   Quartz because it is very durable and,
   Clay because they are weathered silicates
           DETRITAL ROCKS
   Names are based upon sediment particle size
   Sediments can range from microscopic dust
    specks to large house size boulders




        Sand grains           Boulder size sediments
           DETRITAL ROCKS
   Conglomerate – a
    sed rock with large
    rounded particles of
    varying sizes


   Breccia – a sed
    rock that has large
    jagged-edge
    particles of varying
    sizes
            DETRITAL ROCKS
   Sandstone – sed rock
    that has uniform sand
    grain size particles
    only




   Shale – sed rock that
    has very fine grained
    particles, the particles
    are usually flat and
    platy
           Energy of Transport
   The size of the sediment will tell how much
    energy was present when the rock was formed in
    the past

   The larger the sediment sizes = the higher the
    energy required to transport the particles

   Examples: conglomerate and breccia rocks could
    only have formed in high energy environments;
    whereas, shale and sandstone will usually form in
    much lower energy environments
          Energetic Environments
   Low energy depositional
    environments might
    include lakes, ponds, bays,
    and small streams




   High energy environments
    might include raging
    rivers, flood prone areas,
    and glaciers
            Zones of Deposition




High energy environments might include the steep mountain slopes,
rushing rivers, and the rugged continental shelf
Low energy zones would include lakes, lagoons, swamps, and the deep
ocean floor
           CHEMICAL ROCKS
   These are different from detrital rocks in that
    the sediments are already dissolved in water

   The sediments then precipitate out of that
    water to form a rock

                      Three types:


EVAPORITES          BIOCHEMICAL          COAL
            CHEMICAL ROCKS
   Evaporites – rocks
    form when a sea or
    lake dries up and
    leaves behind
    minerals
    – Sometimes these
      are called “salt flats”
   Usually halite and          Rocksalt is a common name
                                for the evaporite rock halite
    gypsum are the
    minerals
           CHEMICAL ROCKS
   Biochemical – plants
    and animals in water
    excrete CaCO3 as
    waste or they make
    their shells out of it

   Over time the CaCO3
    will settle and be
    deposited to make
    LIMESTONE
   Most abundant
    chemical sed rock!
        CHEMICAL ROCKS
 Coal – is nothing more than buried
  swamps or buried peat bogs
 Plant material is “cooked” over long time
  spans and transformed into a fossil fuel




           Examples of modern day swamps
            CHEMICAL ROCKS
   Coal can differ depending upon how much it has
    been cooked. The more it is cooked the harder it
    becomes, the more dense it becomes, the less
    water it will have in it, and the cleaner it burns.

   Swamp  Peat  Lignite  Bituminous  Anthracite




                These two charts show how the
                different stages of coal develop
                 CHEMICAL
                  ROCKS

                   We have a lot of
                   Lignite in Texas...




The four
stages of coal
are shown in
progressive
order in this
diagram
How do seds become Sed Rocks?
   There are two main ways that sediments
    can be lithified into sedimentary rocks.

   Remember, “lithified” literally means
    turned into a rock


     Compaction                Cementation


    Shale is the frock used in fracking
            Lithification Part I
   Compaction – seds
    accumulate over
    time, the weight of
    overlying seds
    compress the
    deeper ones, pore
    space in between
    seds reduces and
    the rock is
    squeezed together
            Lithification Part II
   Cementation –
    water percolates
    through pores,
    minerals dissolved
    in the water are left
    behind in the pore
    spaces, these
    minerals now act as
    a glue holding the
    sediments together
       It Looks Like a Sed Rock!
   The most characteristic feature of sedimentary
    rocks are the strata or beds
   Strata – layers of sed rocks that represent a
    specific depositional period --most striking
    feature of sed rock
   Bedding Planes – these separate strata from each
    other and represent the end of one depositional
    period and the beginning of a new one
1000s of feet of strata
                     To Review:
   Sed rocks are made up of        The particle size gives
    weathered particles from         you clues to the energy of
    other pre-existing rocks         the past environment
   Sed rocks can tell a vivid      Chemical rocks are
                                     named by the process
    story of the past
                                     that forms them
   The two types of sed            Lithification can occur
    rocks are Detrital &             either by compaction or
    Chemical                         by cementation
   Detrital rocks are named        Strata is the most
    by the particle size             distinguishing feature of
                                     sedimentary rocks
METAMORPHIC
   ROCKS
  Rocks of Change
The Keys to Metamorphic Rocks
   Remember, “metamorphism” literally means to
    change form

   How does the original parent rock change??
     The size, the shape, the texture, and even the
    chemistry of the minerals can change!

   Which kind of rocks can be changed into a
    metamorphic rock? All Types:
    – Igneous rocks can be changed
    – Sedimentary rocks can be changed
    – Even metamorphic rocks can be changed into other
      kinds of metamorphic rocks
                Meta-why?
   What causes a rock to change?

   Three factors:
    1. Pressure from deep burial
    2. Heat from deep burial or a nearby
       magma body
    3. Chemically active fluids percolating
       through the rock (we don’t get into this)
                 Meta-how much?
   2 levels of Metamorphism

   Low-grade metamorphism
    – hardly changed from the
      original parent rock

   High-grade metamorphism
    – cannot even recognize the
      original parent rock




                                  The hotter and deeper the
                                  rocks go the greater the
                                  metamorphism will be
        Different types of Change

   There are 3 types of metamorphism:
    –   Burial    Contact     Regional
         Burial Metamorphism
   Burial
    Metamorphism –
    usually a low grade
    change due to
    pressure caused by
    shallow to medium
    burial; heat is not
    a major factor        Burial Metamorphism will
                          not drastically change the
                          parent rock
        Contact Metamorphism
   Contact Metamorphism – also usually a
    low grade change; the parent rock comes
    in contact with a magma body and gets
    cooked enough to metamorphose




                                          Contact
                                          Metamorphism




      Rising magma bodies will metamorphose nearby rocks
        Regional Metamorphism
   Regional Metamorphism – both heat and
    pressure change rock on a grand scale;
    this usually occurs during major tectonic
    events such as mountain building



        Regional
        Metamorphism




The highest grade of change will occur during regional metamorphism
         Texture You Say?
   2 types of texture for metamorphic
    rocks

   Foliated          Non-Foliated
              Foliated Texture
   In Foliated rocks
    mineral grains align
    parallel because of the
    pressure & heat
   This recrystallized
    mineral alignment
    causes the rock to
    have a banded look
   Rocks with multiple
    mineral types will
    exhibit this texture

                              Notice the foliation of
                              this gneiss sample
           Non-Foliated Texture
   In Non-Foliated rocks
    the minerals do not
    line up parallel
   These rocks have a
    uniform appearance
    and no banding
   Rocks that have only
    one kind of mineral
    will usually exhibit this
    metamorphic texture


                                Non-Foliated rocks do not
                                have banding in them
       Naming & Classifying
       Metamorphic Rocks
 We can group these into the two
 categories based upon the types of
 texture the rocks exhibit

 Foliated Rocks   Non-Foliated Rocks
 •Slate           •Marble
 •Schist          •Quartzite
 •Gneiss          •Anthracite
         Naming Foliated Rocks
   Slate – a low grade
    metamorphism of the
    parent rock shale
   The thin platy mica
    flakes line up and give
    the rock foliation
   Slate has great “rock
    cleavage” and it used
    as roof & floor tile,     Slate is a low grade
                              metamorphic rock which
    chalkboards, and          was once used as hand held
    billiard table tops       chalk boards in schools
         Naming Foliated Rocks
   Schist – higher grade
    metamorphism of the
    rock slate
   Schist is “platy” due to
    the mica minerals,
    and it can be split into
    flakes & slabs
   Schist is a high grade
    metamorphic change         Schist is a high grade
                               metamorphic rock with
                               obvious foliation
         Naming Foliated Rocks
   Gneiss (“nice”) – A
    foliated rock from the
    parent rock granite
   Minerals are banded,
    but instead of being
    platy like schist, they
    are granular and
    rounded
   Gneiss is a very high     Notice the good
    grade metamorphic         foliation in this
                              sample of gneiss
    change
     Naming Non-Foliated Rocks
   Marble – coarse
    grained crystalline
    rock from the parent       New reduced
    rock limestone             price! It’s Jesus!!!
   It has large crystals of
    interlocking calcite
   Calcite has a hardness
    of 3 so it is relatively             The calcite crystals
                                         that make up
    soft and great for                   limestone do not
                                         change drastically
    carving and sculpting                when marble is
                                         made; if anything,
   Marble is a low-med                  they will grow in
    metamorphic change                   size as they fuse
                                         together
     Naming Non-Foliated Rocks
   Quartzite – very hard
    rock made from the
    parent rock sandstone
   With heat/pressure
    the quartz grains
    simply fuse together
   Quartzite is a
                            The rock quartzite is
    medium-high grade       not too different than
    metamorphic change      a large quartz crystal
     Naming Non-Foliated Rocks
   Anthracite – the
    highest grade of coal
   It forms from the
    continued cooking of
    bituminous coal
   Anthracite is a high
    grade metamorphism,
    it is extremely hard,
    and it burns almost
    completely clean

                            Both of these anthracite
                            samples are hard and shiny
   Naming Metamorphic Rocks
Metamorphic    Parent       Grade of      Foliated or
 Rock Name      Rock      Metamorphism   Non-Foliated

  Slate         Shale         Low          Foliated

  Schist        Slate         High         Foliated

  Gneiss       Granite      Very high      Foliated

 Marble       Limestone     Low-Med      Non-Foliated

Quartzite     Sandstone     Med-High     Non-Foliated

Anthracite    Bit. Coal       High       Non-Foliated
                 To Review:
 All aspects of a rock       There are two types
  can change during            of textures in
  metamorphism                 metamorphic rocks:
 All rock types can           foliated & non-foliated
  undergo metamorphism        Foliated rocks look
 Heat, pressure, and          banded due to mineral
  fluids do the changing       alignment
 There are three types       Non-foliated rocks do
  of metamorphism: burial,     not look banded
  contact, & regional         Learn the six rocks!

								
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