Rock Basics

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Rock Basicsbackground to understand Earths
landscapes
The Wave Western Australia
The Wave Utah
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Rock Basics Background to understand Earths
landscapes

• Topic 1. Composition of Continental Crust
• Topic 2. Introduction to Minerals
• Topic 3. Basic Rock Types
• Topic 4. Details on Igneous Rocks
• Topic 5. Details on Sedimentary Rocks
• Topic 6. Details on Metamorphic Rocks
• Topic 7. Trying to think like a geologist

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• Annenberg www.learner.org/resources/series78.html

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Topic 1. Composition of the Continental Crust

• O- Oxygen 47
• Si- Silicon 28
• These together 75 of continental crust
• Al- Aluminum 8.1
• Fe- Iron 5.0
• Ca- Calcium 3.6 - nutrient
• Na- Sodium 2.8 - nutrient
• K - Potassium 2.6 - nutrient
• Mg- Magnesium 2.1 - nutrient

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How much do you consume?

• 40,000 pounds Earth/year!
• In a lifetime
• 1050 pounds of lead
• 1050 pounds of zinc
• 1750 pounds of copper
• 4550 pounds of aluminum
• 91,000 pounds of iron
• 360,500 pounds of coal
• 1 million pounds of industrial minerals (calcite,
  clay, borate)

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Topic 2. Introduction to Minerals
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Examples

• Silicates -- have Si as base, Quartz (Si02) -
  obvious 75
• Feldspars- have Si and Al -- and when add (Ca, K,
  Na), you get Feldspars
• Clay minerals that stick to your boot and have
  layered structures

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Topic 3. Basic Rock Types

• IGNEOUS SEDIMENTARY METAMORPHIC

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Igneous (made by fire) - Solidified from molten
rock (i.e., magma). Sedimentary - Deposited and
buried close to Earths surface. Metamorphic
(changed form) - Transformed from preexisting
rocks under high pressure, temperature fluids.
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Rocks

• A rock is a naturally occurring, solid aggregate
  of minerals.

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Rock Types
Sediments make up 75 surface area
Sedimentary rocks are most abundant near Earths
surface - poor preservation Igneous and
Metamorphic rocks make up most of the crustal
volume - limited exposure
Sediments make up only 5 by volume
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Topic 4. Details on Igneous Rocks

• Minerals crystallize from melt, derived from deep
  within Earths crust or mantle
• High temperatures, 700 C more
• Crystal size depends on cooling rate.
• Intrusive rocks cool slowly within deep magma
  chambers
• Coarse, interlocking crystals
• Extrusive rocks cool rapidly at (or near) the
  surface of the earth
• Fine-grained, often glassy

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Igneous Rocks
Common in volcanic areas plate boundaries
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Least Silicon (Mafic) Diorite Most Silicon
(Felsic)
Gabbro Diorite Granite
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Classroom Resources

• Extrusive Igneous (lava) Hawaii Basalt Flow
• aa flow pahoehoe flow

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• Intrusive igneous magma chamber - Pluton

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Roof pendant (dark metamorphosed sedimentary
rock) comprised of remnant country rock is
draped over the younger intruded Sierra Nevada
batholith (light colored granodiorite).
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Basalt
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Topic 5. Details on Sedimentary Rocks

• Loose particles (sand, silt, marine shells)
  accumulate on shorelines, basins, rivers, etc.,
• Clastic Sediments
• Minerals precipitate from dissolved chemicals in
  water
• Chemical Biochemical Sediments
• All are the products of Weathering - that breaks
  up and decays rocks, and Erosion - that
  transports from source to point of deposition

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Common along passive margins (and other basins)
Weathering Erosion
Transport
Basement Rocks
Clastic Sandstone
Deposition
Chemical Rock Salt
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Lithification
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• Shale

Conglomerate
Sandstone
Breccia
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Large to Small
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Sedimentary Silicates (esp. Clays) Carbonates Su
lfates Halides (Precipitates)
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Topic 6. Details on Metamorphic Rocks

• High temperatures and pressures at depth cause
  changes in mineralogy, texture, and composition
• Changes take place in Solid State by
  recrystallization and chemical reactions
• Temperatures greater than 250, less than 700
• Regional Metamorphism - High pressures and
  temperatures derive from regional collision,
  deformation and mountain building.
• Contact Metamorphism - Locally high temperatures,
  adjacent to intrusions.

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Metamorphic Rocks
Common at convergent plate boundaries
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Metamorphic Rocks
Fig 4.6

• Foliations - Planar fabric defined by
• Alignment of platy minerals (micas clays)
• Alternating bands of mineral types
• Indicative of high pressures and deformation
  during formation
• Pressure-Temperature-time paths

• Not Foliated
• Distinct low- pressure minerals

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Classroom Resources

• Showing mineral re-alignment into foliations

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• Metamorphic
• Silicates predominate
• Due to silicate source rocks
• Distinctive mineral types indicative of solid
  state reactions

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Typical Rock Types Seen by Geologic Origin
Sedimentary Types
Metamorphic
Igneous Types
Grain Aspects Clastic Solution (carbonate) Foliated Non-Foliated Intrusive Extrusive
Coarse Conglomerate Breccia Limestone Dolomite Gneiss Marble Granite Gabbro Diorite
Medium Sandstone Siltsone Limestone Dolomite Schist Phyllite Quartzite
Fine Shale (Mudstone) Calcareous Mudstone And Chert Slate Amphibolite Basalt Rhylite Obsidian
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Topic 7. Trying to think like a geologist

• Thinking in terms of sequences
• Classroom Resources Animations

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What came first? Next? Last?
Last
Disconformity a time when deposition
temporarily stopped
great unconformity Showing uplift then erosion

• First

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Great Unconformity
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The Rock Cycle

• Melting Intrusion
• Solidification of melt
• Mountain Building
• Uplift Exposure
• Weathering
• Erosion Transport
• Deposition Burial
• Metamorphism
• Melting Intrusion

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Online Resource

• Rock Cycle
• http//serc.carleton.edu/NAGTWorkshops/visualizati
  on/collections/rock_cycle.html

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Geologic Time Getting a year timeline has been
only recently

• In Classroom Resources Folder, clip about
  figuring out age of Earth

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Geologic Time

• Large blocks of time represented by changes in
  evolution

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Classroom Resource

• Geologic Time as Football Field

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• Toilet Paper Used to Grasp Time Depth
• http//serc.carleton.edu/quantskills/activities/TP
  GeoTime.html

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Review

• Continental Crust O, Si, Al, Fe, traces
• Minerals specific chemical crystalline
  structures
• Rocks combination of minerals
• Main rock types igneous, sedimentary,
  metamorphic felsic light-colored, mafic
  dark-colored
• Rocks go through a cycle
• Geologic time is VERY long timeframe...