What is a Rock

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What is a Rock?

• A rock is a
• Naturally formed,
• Consolidated material,
• Composed of grains of one or more minerals.

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Some Rocks
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Types of Common Rocks

• There are three types of common rocks
• Igneous rock
• Sedimentary rock
• Metamorphic rock

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Igneous Rock

• Igneous rocks form from the solidification of
  magma.
• Ex pumice, obsidian

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Identifying Igneous Rocks

• Where the igneous rock forms in the crust shapes
  their composition so igneous rocks are identified
  by their texture.
• Extrusive rocks form at or near the surface and
  are fine-grained.
• Intrusive rocks form below the surface and are
  coarse-grained.

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Basalt Igneous Extrusive, Fine-grained
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Granite Igneous Intrusive, Coarse-grained
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Igneous Rock Features Felsic

• Felsic rocks are rich in potassium feldspar and
  quartz and are light in color.
• Example is the granite family of rocks.
• Felsic rocks are most common in the continents.

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Felsic Igneous Rocks
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Igneous Rock Features Mafic

• Mafic rocks are rich in dark plagioclase feldspar
  and pyroxene.
• Example the gabbro family of rocks.
• Mafic rocks are more common in the ocean basins.

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Mafic Igneous Rocks
Basalt
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Igneous Identification

• Some igneous rocks have holes in them that formed
  during the cooling of the magma. These types are
  said to be vesicular.

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Igneous Rocks
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Structure of Igneous Rocks

• Shield and Cinder Cone volcanoes will erupt and
  create lava flows, and lava plateaus, that form
  igneous rocks.
• When magma does not erupt but instead forces its
  way up through cracks and faults it produces
  large masses of intrusive rock called plutons.

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Shield (Etna) and Cinder Cone (Paracutin)
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Plutons

• Plutons are classified according to size
• Sills are slabs of igneous rock parallel to the
  rocks they intrude
• Dikes are slabs of igneous rock that cut across
  the rock layers they intrude
• A laccollith forms between two rock layers,
  bulging up to form a dome
• A batholith is the largest intrusion and they
  form the core of many mountain ranges.
• When a volcano erodes the harder volcanic neck is
  often left behind.

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Devils Tower is the result of igneous rock that
was underground until all the weaker surrounding
rock was eroded