Miss Rachel Trucks

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Metamorphic Rocks

• Miss Rachel Trucks
• Earth Science
• Grade 10

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Why Study Metamorphic Rocks?

• Metamorphic Rocks are a key to the early history
  of Earth.
• Metamorphic Rocks can help us find important
  economic resources.
• Metamorphic Rocks also can be used in artistic
  endeavors.

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What are Metamorphic Rocks?

• Meta Change and MorphShape or form. Metamorphic
  Rocks are rocks that transform from other rocks
  or minerals. This generally happens beneath the
  Earths surface. They are subject to heat,
  pressure and fluid activity.

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Agents of Metamorphism
Heat
Pressure
Fluid Activity
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Agents of Metamorphism

• Heat
• Heat increases the rate of chemical reactions to
  produce new mineral assemblages.
• Geothermal gradient- temperature increases with
  depth at a rate of 20 - 30 degrees C per km in
  the crust.
• Increase of temperature and pressure with depth
  causes Regional Metamorphism
• Heat may come from large bodies of molten rock
  rising under a wide geographic area.
• Intrusions of hot magma can bake rocks as it
  intrudes them. Lava flows can also bake rocks on
  the ground surface.
• Lava or magma in contact with other rock causes
  Contact Metamorphism.

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Agents of Metamorphism

• Fluid Activity
• In some metamorphic settings, new materials are
  introduced by the action of hydrothermal
  solutions (hot water with dissolved ions). Many
  metallic ore deposits form in this way.
• Hydrothermal solutions associated with magma
  bodies
• Black smokers - Sea water percolates through
  newly formed oceanic crust, dissolving out
  metallic sulfide minerals. The hot sea water
  rises along fractures and pours from vents in the
  seafloor as black clouds of dark mineral-rich
  water. Sulfide minerals (such as pyrite,
  sphalerite, and galena) and copper precipitate
  when the hot water comes in contact with cold sea
  water.

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Agents of Metamorphism

• Pressure
• Burial Pressure. Pressure increases with depth
  due to the weight of the overlying rocks. A cubic
  foot of granite weighs 167.9 pounds. Increase of
  pressure and temperature with depth causes
  Regional Metamorphism.
• Lithostatic Pressure is pressure that is applied
  equally in all directions on the rock, it tends
  to compress them.
• Differential Pressure is pressure applied
  unequally on a body of rocks, minerals align
  parallel to each other.
• Tectonic pressures associated with convergent
  plate boundaries and continental collision also
  cause Regional Metamorphism.
• Rocks formed along fault zones are called
  mylonites.

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Formation of Metamorphic Rocks
Here is a picture diagram of how metamorphic
rocks are formed.
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How do you classify Metamorphic Rocks?

• Metamorphic rocks are classified by their
  texture. There are two different types Foliated
  Metamorphic Rocks and Nonfoliated Metamorphic
  Rocks.

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Foliated Metamorphic Rocks

• Foliated metamorphic rocks are those that arrange
  in a parallel fashion.
• Slate - very fine grained rock. Resembles shale.
  Has slaty cleavage which may be at an angle to
  the original bedding. Relict bedding may be seen
  on cleavage planes. Often dark gray in color.
  "Rings" when you strike it.
• Schist - metamorphic rock containing abundant
  obvious micas, several millimeters across.
  Several types of schist may be recognized, based
  on minerals which may be present
• Gneiss - (pronounced "nice") - a banded or
  striped rock with alternating layers of dark and
  light minerals. The dark layers commonly contain
  biotite, and the light layers commonly contain
  quartz and feldspar.

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Nonfoliated Metamorphic Rocks

• Mosaic of roughly equi-dimensional mnerals. They
  are a result of contact or regional metamorphism.
• Marble - fizzes in acid because its dominant
  minerals is calcite (or dolomite). The parent
  rock is limestone (or dolostone).
• Quartzite - interlocking grains of quartz.
  Scratches glass. The rock fractures through the
  grains (rather than between the grains as it does
  in sandstone). The parent rock is quartz
  sandstone.

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Can You Do It?

• Can you classify the following rocks?
• Gneiss
• Schist
• Slate
• Marble
• Quartzite
• Click the button to the left to try your skills!!

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Resources

• mailtohttp//www.science.ubc.ca/geol202/meta/met
  adef.html
• Georgia Perimeter College, Clarkston, GA
• pgore_at_gpc.peachnet.edu

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