Rocks

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Rocks
Are composed of more than one mineral
Chapter 6 Section 1
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Three Major Classes of Rocks

• 1. Igneous-formed by cooling and hardening of
  hot, molten rock (magma) inside Earth

2. Sedimentary-formed by the compaction and
cementing of layers of sediments (rock fragments,
plant and animal remains, minerals that settle
out of solution onto lake and ocean bottoms)
3. Metamorphic-formed by the effects of heat and
pressure on other rocks
BrainPop 3 Types of Rocks
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The Rock Cycle

• The continuous process that causes rocks to
  change from one form to another
• Caused by interactions between water, air, and
  land

Rock Cycle Movie
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ESRT pg. 6
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What happens to igneous rocks?
1. Heat and pressure/ metamorphism?
metamorphic rock 2. Melt to form magma which
solidifies ? igneous rock 3. Weathering and
erosion form sediments which are deposited,
buried, compacted, and cemented? sedimentary rock
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What happens to sedimentary rocks?
1. Heat and pressure/ metamorphism?
metamorphic rock 2. Melt to form magma which
solidifies ? igneous rock 3. Weathering and
erosion form sediments which are deposited,
buried, compacted, and cemented? sedimentary rock
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What happens to metamorphic rocks?
1. Heat and pressure/ metamorphism?
metamorphic rock 2. Melt to form magma which
solidifies ? igneous rock 3. Weathering and
erosion form sediments which are deposited,
buried, compacted, and cemented? sedimentary rock
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Igneous Rocks

• Form from molten rock or volcanic ash
• As magma cools, crystals grow interlock (rate
  affects size)

Chapter 6 Section 2
Igneous Rock Formation Movie
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The Starting Material

• Magma may be classified as felsic, mafic, or an
  intermediate form.
• Felsic magma thick and slow moving large
  amounts of silica (SiO2) and small amounts of
  calcium, iron, and magnesium typically hardens
  into rocks containing light-colored silicate
  minerals (ex. quartz and orthoclase feldspar)
• Mafic magma hotter, thinner, more fluid large
  amounts of iron and magnesium and smaller amounts
  of silica typically hardens into rocks
  containing dark-colored silicate minerals (ex.
  hornblende, augite, biotite)

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2 Groups of Igneous Rocks
Intrusive Igneous Rocks

• Form from magma which cools slowly deep inside
  the earth (internal)
• Crystals are medium to coarse texture (easily
  seen)
• Form from lava (magma that has exited the crust)
  that cools quickly (external)
• Crystals are very small or not seen at all

Extrusive Igneous Rocks
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Igneous Rock Descriptions

• Igneous Rocks are grouped into families according
  to mineral composition.
• Specific igneous rocks can be recognized by

Color- determined by the mineral
composition (makeup)
Texture- the size arrangement of crystals
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Granite Family/Felsic Rocks

• Form from felsic (silica and aluminum-rich)
  magmas
• Usually coarse-grained because their slow-rising,
  sticky parent magmas tend to cool slowly
  underground
• Typically contain quartz, feldspar, mica,
  hornblende
• Light-colored
• Low in density

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Granite Family/Felsic Rocks

• Granite
• one of the coarsest-grained
• rocks in this family
• Intrusive
• Often contain large amounts of light-colored
  feldspar
• color of feldspar determines color of the rock
• Usually ranges from white or gray to pink
• Very common continental rock found in many
  mountainous areas across the U. S.

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Granite Family/Felsic Rocks

• Obsidian
• Extrusive
• Glassy texture (no crystals)
• Chemically similar to granitic rocks
• even though it is usually dark brown or black
• Pumice
• Extrusive
• Forms when silica-rich lava
• hardens as steam other gases bubble out of it
• Vesicular texture
• Resembles a sponge because of holes and air
  pockets
• Often able to float on water

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Granite Family/Felsic Rocks

• Felsite
• General name for any light-colored, fine-grained
  rock
• Rhyolite is a common example
• Fine-grained, ranges from light gray to pink

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Gabbro Family/Mafic Rocks

• Form from mafic (iron and magnesium-rich/silica
  poor) magmas
• Dark in color
• High density
• Typically contain pyroxene, olivine, plagioclase
  feldspar (amphibole and biotite mica)

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Gabbro Family/Mafic Rocks

• Gabbro coarse-grained
• rock. very dark color
• Basalt fine-grained, dark gray or black
• Composition similar to gabbro
• Most common rock in gabbro family
• Makes up the ocean floor
• On land, most common rock
• formed from lava flows

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Gabbro Family/Mafic Rocks

• Diabase texture is finer than gabbro but coarser
  than basalt
• Basalt glass resembles obsidian but is mafic
• Scoria (like pumice) full of holes,
• darker and denser than pumice, holes are
  usually larger, unlikely to float

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Diorite Family/Intermediate Rocks

• Composition is neither felsic or mafic but has
  characteristics of both intermediate
• Colors tend to be medium grays and greens (darker
  than granites and lighter than gabbros)

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Diorite Family/Intermediate Rocks

• Diorite coarse-grained, has less quartz than
  granite and less plagioclase feldspar than gabbro
• Andesite
• fine-grained

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Other Igneous Rocks

• Felsic-intermediate granodiorite
• Ultramafic peridotite, dunite, pyroxenite
• Hypothesized to be similar to rocks in Earths
  mantle

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Igneous Intrusions

• Pluton any rock mass that forms when magma
  pushes into fractures (cracks) in the bedrock
• Dike vertical, in between rock layers
• Sill parallel to rock layers it intrudes
• Ex. Palisades Sill along the Hudson River (NY/NJ)
• Laccolith domed mass, bulge
• Volcanic neck central plug of hardened magma
  left after the volcanic material around it has
  worn away
• Batholith largest of all plutons, cores of many
  mountains
• Stock a small batholith that is exposed at the
  surface

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Igneous Intrusions
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Sedimentary Rocks

• Made of sediments
• Cover most of the crusts surface
• 3 types

Chapter 6 Section 3
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Clastic Sedimentary Rocks

• Formed from fragments of other rock that are
  moved (usually by running water)
• Sediments are deposited layer after layer (as the
  water slows down)
• Sorted by largest sediments first, smallest last
• Compacted as layers pile up or cemented together
  by minerals that are dissolved in the water
• Type of cement influences color (silica, calcite,
  iron oxide, and clay)

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Classified by Particle Size

• Smallest
• Silt Clay particles
• ?shale/siltstone
• Sand particles
• ?sandstone
• Mixed particles
• ?conglomerate/breccia
• Largest

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Chemical Sedimentary Rocks

• Chemical sediments form when minerals precipitate
  (fall out) of water.
• Two ways
• Evaporation Form when a sea or lake dries up
  leaving behind minerals that were dissolved in
  water
• Chemical action dissolved ions combine to form
  new minerals

Also referred to as crystalline sedimentary rocks
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Chemical Sedimentary Rocks

• Examples
• Rock Salt
• Rock Gypsum
• Limestone (travertine)

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Organic Sedimentary Rocks

• Form from sediments consisting of the remains of
  plants and animals

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Organic Sedimentary Rocks

• Shells
• ? Fossil
• limestone

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Organic Sedimentary Rocks

• Plant remains ? coal

peat
lignite
anthracite
bituminous
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Features of Sedimentary Rocks

• Stratification
• arrangement of visible layers
• result from changes in sediment type being
  deposited
• Bedding planes (lines between the layers) show
  where the layers are separated
• Usually horizontal, but cross-bedding (angled
  deposits) can occur
• Occur for a number of reasons
• New types of rocks picked up (from different
  locations)
• More of different types of rocks carried during
  flooding
• Sediments carried longer or shorter distances

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Features of Sedimentary Rocks

• Fossils
• the remains, impression, or other evidence of a
  plant or animal preserved in rock
• occur when dead organism is buried by sediments
  and gradually turns to rock
• Usually only hard parts are preserved
• Impressions occur when shell, skeleton, etc. is
  pressed into soft sediments

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Features of Sedimentary Rocks

• Ripple marks sand patterns formed by the wind,
  streams, waves, or currents
• Mud cracks develop when wet clay dries and
  contracts (shrinks)
• Cracks fill with different sediments fossilize

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Features of Sedimentary Rocks

• Nodules lumps of fine-grained silica in
  limestone or chalk
• Ex. chert and flint
• Concretions round, solid masses of calcium
  carbonate
• Probably form when minerals in dissolved in water
  precipitate around shell fragments or other
  impurities in clay sediments
• Ex. oolites
• Geodes spheres of silica rock
• found in limestone
• Inside lined or filled with crystals
• (quartz or calcite)

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Metamorphic Rocks

• Formed from parent rock
• Often resembles parent rock
• Differences are the result of metamorphic
  processes that the parent rock has undergone

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Metamorphic Processes

• Metamorphism the process by which a rocks
  structure is changed by pressure, heat, and
  moisture.
• Pressure heat may originate from
• the Earths internal heat
• the weight of overlying rock
• the deformation of rock as mountains build

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Metamorphic Processes

• A metamorphic rock may have a chemical
  composition, texture, or internal structure that
  differs from the parent rock.
• Minerals may be enlarged or reformed
• New minerals may appear
• The rock may be more dense and less porous (less
  empty space)

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Metamorphic Processes Two Basic Types of
Metamorphism

• Regional
• Forms most of the metamorphic rock of Earth's
  crust
• Often occurs over very large areas
• Local
• Smaller, more distinct areas

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Regional Metamorphism

• Can occur during mountain building
• Large areas of rock metamorphosed
• Due to intense heat and pressure
• Temperature increases with depth
• Pressure increases w/ depth (more overlying rock)
• Pressure greater in 1 direction, minerals align
  in layers
• Hot liquids gases speed up the process
• Different amounts of heat pressure ? different
  amounts of metamorphism.
• Can cause folding of rock layers
• Higher temperature pressure ? greater
  metamorphism

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quartzite
sandstone
gneiss
schist
phyllite
slate
shale
Lime
Marble
Limestone
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Local Metamorphism

• Two types
• Contact
• Occurs when hot magma moves into rock, heating
  and changing it.
• Causes fewer changes and affects much less rock
  than regional metamorphism
• Deformational
• Occurs at relatively low temperatures and high
  pressure
• Caused by stress and friction (often at faults
  where rocks move against each other)
• Mineral composition usually stays the same, but
  texture and structure may change

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Metamorphic Rock Descriptions

• Description and identification usually based on
  parent rock, mineral content, and texture
• 2 types
• Foliated
• Non-foliated

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Metamorphic Rock Descriptions

• Foliated Metamorphic Rocks
• Minerals flattened by pressure producing mineral
  alignment or (different colored) bands
• May look scaly
• Often split along parallel layers

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Foliated Metamorphic Rocks Examples
Granite ? gneiss Shale ? Slate ? Phyllite ?
Schist
(Extreme Metamorphism)
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Metamorphic Rock Descriptions

• Nonfoliated Metamorphic Rocks
• Dont show banding
• look crystalline (sparkles)

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Nonfoliated Metamorphic Rocks Examples

• Limestone ? marble
• Sandstone ? quartzite
• Conglomerate ? metaconglomerate

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