Rock Cycle

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Rock Cycle Igneous Rocks

• Chapter 5

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Minerals vs. Rocks

• Minerals are homogeneous, naturally occurring,
  inorganic solids.
• Each mineral has a definite chemical composition
  and a characteristic crystalline structure.
• A mineral may be a single element such as copper
  (Cu) or gold (Au), or it may be a compound made
  up of a number of elements.
• About 3,500 different minerals have been
  described, but only about 24 are common.
• Rocks are made up of one or more minerals.

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Three Types of Rocks

• Igneous Rocks Formed from the cooling of molten
  rock.
• Sedimentary Rocks Formed in layers as the
  result of moderate pressure on accumulated
  sediments.
• 3. Metamorphic Rocks Formed from older "parent"
  rock (either igneous or sedimentary) under
  intense heat and/or pressure at considerable
  depths beneath the earth's surface.

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The Rock Cycle

• The inter-relationship among the rock types is
  called
• THE ROCK CYCLE.
• Basically a recycling machine of rocks.

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http//science.cc.uwf.edu/sh/curr/rockcyc/rockcyc.
htm
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Stop here for 1st Lecture

• Show Rock Cycle Video

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Igneous Rocks

• Igneous rocks are called fire rocks and are
  formed either underground or above ground.
• Underground, they are formed when the melted
  rock, called magma, deep within the earth becomes
  trapped in small pockets. As these pockets of
  magma cool slowly underground, the magma becomes
  igneous rocks.
• Also formed when volcanoes erupt, causing the
  magma to rise above the earth's surface. When
  magma appears above the earth, it is called lava.
  Igneous rocks are formed as the lava cools above
  ground.

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Igneous Illustration
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Magma

• Magma is liquid and usually less dense than the
  surrounding solid rock
• As it moves upward to cooler regions of the
  Earth, it crystallizes into an igneous rock.
• Magma can cool on the Earth's surface, where it
  has erupted from a volcano called extrusive rock
• Or under the Earth's surface, where it has
  intruded older rocks called intrusive rock.
• The composition of magma is limited to the eight
  common elements of the earth's crust and combine
  within a melt to form silicate minerals.
• These silicate minerals include
• feldspars (plagioclase feldspar, potassium
  feldspar)
• quartz
• micas (muscovite, biotite)
• pyroxenes (augite)
• amphiboles (hornblende)
• olivine
• These minerals make up over 95 of the volume of
  the common igneous rocks, making igneous rocks
  easy to identify.

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Extrusive Igneous Rock
Extrusive igneous rocks form when magma reaches
the Earth's surface a volcano and cools quickly.
Most extrusive (volcanic) rocks have small
crystals. Examples include basalt, rhyolite, and
andesite.
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Intrusive Igneous Rock

• Intrusive, or plutonic, igneous rocks form when
  magma cools slowly below the Earth's surface.
  Most intrusive rocks have large, well-formed
  crystals.
• Examples include granite, gabbro, and diorite

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How to tell if you have an igneous rock

• Igneous rocks are recognized by
• the interlocking texture of the grains
• the presence of vesicules (holes) in extrusive
  igneous rocks
• may be dark-colored and heavy
• may display two grain sizes, one much larger than
  the other

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Bowens Reaction Series
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Steps in Identification

• Use Bowens Scale to determine identity of
  igneous rocks.
• Determine the color (indicates mineral
  composition)
• Determine the texture (indicates cooling history)
  
• Phaneriticlarge grains
• Aphaniticsmall grains (too small to identify
  with the naked eye)
• Porphyriticfine grains mixed with larger grains
• Glassyglass-like
• Vesicularholes
• Example A light-colored, fine-grained
  rockrhyolite

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Textures
EXTRUSIVE
INTRUSIVE
Coarse grained (phaneritic) Slow cooling
Fine grained (aphanitic) Fast cooling
Porphyritic Two phases of coolingone slow,one
fast
Porphyritic Two phases of coolingone very
slow, one slow
Pegmatitic Slow cooling plus high water content
Glassy Fast cooling plus high silica content

3rd Type Volcanic vesicular (bubbles/holes)

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Igneous Composition

• Ultramafic rocks are dominated by olivine and/or
  pyroxene.
• Mafic rocks are dominated by plagioclase and
  pyroxene (even if you can't see them with the
  naked eye) and smaller amounts of olivine.
• Intermediate rocks are roughly even mixtures of
  felsic minerals (mainly plagioclase) and mafic
  minerals (mainly hornblende, pyroxene, and/or
  biotite). There is little or no quartz.
• Felsic rocks are mostly feldspar (especially
  K-feldspar), at least 10 quartz, and less than
  15 mafic minerals (biotite, hornblende).

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INTRUSIVE COMPOSITIONS
EXTRUSIVE COMPOSITIONS
Peridotite Ultramafic
Rare occasions only. We will not learn these.
Gabbro Mafic
Basalt Mafic
Diorite Intermediate
Andesite Intermediate
Granite Felsic
Rhyolite Felsic