Rocks-Chapter 9

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Rocks-Chapter 9
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The Rock Cycle
The rock cycle is a general model that describes
how various geological processes create, modify,
and influence rocks
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• How does an igneous rock become sedimentary?
• How do sedimentary rocks become metamorphic?

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The Rock Cycle
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James Hutton

• Recognized the rock cycle 1788
• Observed Siccar Point, Scotland
• Tilted and Partially Eroded, Younger rocks are
  horizontal

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Rocks

• Essential Minerals-minerals that always occur in
  a rock
• Quartz, orthoclase feldspar, plagioclase
  feldspar, augite and olivine
• Accessory Minerals-minerals that sometimes occur
  in a rock
• Micas and amphibole (hornblende)

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Rock Forming Minerals
Augite
Hornblende
Mica
Orthoclase
Plagioclase
Quartz
Feldspars
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Igneous Rocks

• Rocks formed from molten rock that cools and
  hardens

Granite
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Sedimentary Rocks

• Rock formed when sediments are pressed and
  cemented together

Sandstone
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Metamorphic Rock

• Rock formed when rocks are placed under heat and
  pressure

Gneiss
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Igneous Rocks (fire-formed)

• Volcanic/Extrusive-formed from lava (molten rock
  on the surface of the Earth)

Pumice
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Igneous Rocks (fire-formed)

• Plutonic/Intrusive-formed from magma (molten rock
  within the Earth)

Diorite
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Texture

• Coarse-grained-Large crystals-Intrusive
• Fine-grained-Small crystal-extrusive

Granite
Rhyolite
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Texture

• Determined by cooling rate
• Cool Fast-Small Crystals
• Cool Slow-Large Crystals

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Most Common Coarse-Grained Igneous Rock-Granite
(Intrusive)

• Granitic Rocks-Lower density/lighter in color
• Contain more silica/less iron and magnesium
• Granitic magma is stiff and thick

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Most Common Fine-Grained Igneous Rock-Basalt
(Extrusive)

• Basaltic rocks are dark colored and dense
• Contain iron and magnesium/very little silica
• Basaltic lava is thin and flows freely

Basalt
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Andesitic Rocks

• Have more balanced composition of minerals
• Higher density than basaltic or granitic rocks

Andesite
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Pegmatite

• Igneous rock that has crystals over 1 cm in
  diameter

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Prophyry

• Igneous rock with both large and small crystals

Diorite Porphyry
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Igneous Examples
Obsidian-Volcanic Glass
Granite
Basalt
Scoria- Swiss Cheese
Pumice-some float
Gabbro
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Sedimentary Rocks

• Compaction-Rock particles are pressed together
• Cementation-Minerals used as natural glue (Quartz
  and Calcite)

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Types of Sedimentary Rock

• Clastic (fragmental/detrital)
• Made up of rock fragments

Sandstone
Conglomerate
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Types of Sedimentary Rock

• Non-Clastic-Made from once living things or
  chemical processes

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Clastic Rock Fragments
 
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Non-Clastic

• Organic-Made of the remains of once living things

Chert-fossils of Crinoids
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Non-Clastic

• Precipitates- Rock material settle out of
  solution by chemical reaction reaction

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Non-Clastic

• Evaporites-Form when water evaporates and leaves
  rock material behind

Rock Salt
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Sedimentary Examples
Chert
Rock Salt
Limestone
Coquina
Chalk
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Metamorphic Rocks

• Existing Rocks are placed under heat and pressure

Slate
Marble
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Metamorphic Rocks

• Regional Metamorphism-Large land areas (under
  mountain ranges or several states) are changed by
  heat and pressure
• Contact Metamorphism-Rocks are changed when they
  come in contact with molten rock

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Types of Metamorphic Rock

• Foliated-Contains visible bands or layers

Gneiss
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Types of Metamorphic Rock

• Non-Foliated-Contains no bands or layers

Quartzite
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Metamorphic Conditions
 
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Metamorphic Examples
Mica Schist
Garnet Schist
Slate
Quartzite
Amphibolite
Hornfels