PSC 1351

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PSC 1351

• Chapter 17

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Structure of the Earth
Outer Core Liquid (about 2270 km thick)
Crust Solid (5 to 8 km under oceans 10 to 75 km
on continents)
Inner Core Solid (1200 km radius)
Mantle Solid (about 2870 km thick)
This model of the Earths structure is based on
Earthquake data as observed all around the Earth
The liquid outer core will not allow S waves to
penetrate it only P waves. Also, P waves
are refracted as they penetrate the outer core,
leading to shadow zones.
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Most Abundant Elements in the Crust
Element Symbol of
Crust Oxygen O
46.6 Silicon Si
27.7 Aluminum Al
8.1 Iron Fe
5.0 Calcium
Ca 3.6 Sodium
Na 2.8 Potassium
K 2.6 Magnesium
Mg 2.1
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Minerals

• Substances that constitute the basic materials
  for rock formation on the Earths crust. Four
  criteria must be met
• 1) They must be crystalline (crystal structure)
• 2) They must occur naturally
• 3) They must be inorganic
• 4) They must have a specific chemical composition
• Minerals may be subdivided into 2 categories
• A) Silicates (contain (SiO4)-4 , the silica
  tetrahedron)
• B) Nonsilicates

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Silicate Minerals
Ferromagnesian Nonferromagnesian
Clay Minerals Name Structure Name
Structure Name Structure Olivine
isolated tet. Muscovite
Kaolinite Sheet Pyroxene single chain
Mica Sheet Illite
Sheet Biotite Feldspar
Chlorite Sheet
Mica sheet (Plagioclase)
Framework Amphibole double
(Orthoclase) Framework Montmori- (Hornblende)
chain Quartz Framework llonite
Sheet Note Ferromagnesian silicate
minerals are characterized by a darker
color than nonferromagnesian or clay minerals.
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Nonsilicate Minerals (1)
Oxides Sulfides
Sulfates

Hematite (Fe2O3)
Pyrite(FeS2) Gypsum(CaSO4 2H2O))
Magnetite(Fe3O4) Sphalerite(ZnS)
Anhydrite(CaSO4) Ilmenite(FeTiO3)
Galena(PbS) Corundum(Al2O3) Chalcopyrite(Cu2S) (A
l oxides)
Phosphates
Apatite (CaF2 3Ca3(PO4)2 )
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Nonsilicate Minerals (2)
Halides Carbonates
Native Elements Halite (NaCl) Calcite
(CaCO3) Gold (Au) Fluorite
(CaF2) Dolomite (CaCO3 MgCO3) Silver (Ag)

Copper (Cu)

Sulfur (S)

Diamonds (C)
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Mineral Identification Processes

• Crystal Form (isometric, hexagonal, tetragonal,
  orthorhombic, monoclinic, triclinic)
• Color
• Streak (rub mineral on porcelain and note color
  of powder streak produced)
• Luster
• Hardness (according to Mohs hardness scale)
• Cleavage
• Fracture
• Specific gravity (density)

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Mohs Hardness Scale
Examples A fingernail has a hardness of
about 2.5. Therefore, it will scratch gypsum.
Glass has a hardness of about 5.5. Therefore,
calcite will scratch a fingernail, but will not
scratch glass. Quartz will scratch glass.
Material Hardness Talc(H2Mg3(S
iO3)4) 1 (softest) Gypsum(CaSO4
2H2O) 2 Calcite (CaCO3)
3 Fluorite (CaF2)
4 Apatite(CaF2 3Ca3(PO4)2) 5 Orthoclase(KAlSi3
O8) 6 Quartz (SiO2)
7 Topaz(Al2(F,OH)2SiO4)
8 Corundum(Al2O3) 9 Diamond (C)
10 (hardest)
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Crystallization of Minerals (1)

• From magma Bowens Reaction Series
• Temp. ºC
• 1500 Olivine
  Ca rich Plagioclase Feldspar
• Pyroxene (Augite)
• Amphiboles (Hornblende)
• Biotite Mica
  Na rich Plagioclase Feldspar
• 800 Orthoclase
  Feldspar
• 
  Muscovite Mica
• 
  Quartz

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Crystallization of Minerals (2)
B) At Normal Temperatures Most
nonsilicates carbonates, sulfates, oxides,
halides, sulfides C) At above 150ºC and 2000
atmospheres pressure Garnet, talc,
graphite D) Ore Minerals Along fractures
in rocks, called veins pyrite(FeS2),
galena(PbS), sphalerite (ZnS),
fluorite(CaF2), chalcopyrite(CuFeS2)
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Rocks

• Rocks are aggregates of one or more minerals,
  held together with cementing material (like
  calcite or silica).
• Classified as a) igneous b) sedimentary c)
  metamorphic
• Igneous rocks those that crystallize from magma.
  If at surface extrusive (fine texture - example
  rhyolite). If deep within the Earth intrusive
  (coarse texture - example granite).

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Sedimentary Rocks

• Formed when sediment (due to erosion) is
  deposited over long periods of time and is
  compacted (high pressure) and cemented (calcite
  and silica) in the lithification process. Two
  basic types
• a) Clastic (sediments due to weathering)
• b) Chemical (sediments due to inorganic
  processes or biochemical origins)
  

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Clastic Sedimentary Rocks
These rocks are the result of weathering of older
rocks. They are classified according to particle
size Particle Size Sediment Name
Rock Name 2 256 mm
gravel conglomerate or
breccia 1/16 2 mm sand
sandstone 1/256 1/16 mm
silt
siltstone lt 1/256 mm clay
shale, claystone
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Chemical Sedimentary Rocks
The sediments for these rocks are due to either
inorganic processes (evaporation of water in a
lake, gives rise to precipitation of salt
sediments) also called evaporites or due to
biochemical processes (marine animals producing
shells calcite) Mineral Content
Rock Calcite(CaCO3)
Limestone Dolomite(CaCO3
MgCO3) Dolomite Gypsum(CaSO4 2H2O)
Gypsum Halite(NaCl)
Salt
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Metamorphic Rocks
These are previously existing rocks that have
been extensively changed by high temperature
(without melting) and high pressure. Produced by
either Contact Metamorphism (exposure to high
temperature of a nearby magma) or Regional
Metamorphism (due to plate tectonic motion).
These rocks may have either a foliated or
nonfoliated texture.
Parent Pressure Pressure
Pressure Type Rock New Rock
New Rock New Rock Foliated Shale
Slate Schist
Gneiss Nonfoliated Limestone
Marble Nonfoliated Sandstone Quartzite
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The Rock Cycle
Igneous Rock
Sediment
Sedimentary Rock
Magma
Metamorphic Rock