Rocks and Minerals Part 1 Sept. 8

Rocks and Minerals – Part 1

September 8, 2017

Goal:  To identify and explain the processes involved in the formation and classification of metamorphic, sedimentary, and igneous rocks.


  1.  The “rock cycle” is a model that describes the formation, breakdown, and reformation of a rock.
  2. Sedimentary rocks are composed of rounded grains or fragments of other rocks cemented together in layers.  This type of rock may contain fossils.  Sedimentary rocks are usually formed in a water environment like an ocean, lake or stream. Examples: limestone or sandstone.
  3. Sedimentary rocks may be broken down by weathering were weather such as rain, ice or wind, chemicals or plants may create loose material called sediments.
  4. Sediments are deeply buried and placed under great pressure because of the weight of layers of rock and other materials on top of them.  This is called compaction.
  5. Cementation is the term used for new minerals that help to stick the sediments tightly together like cement.
  6. Metamorphic rocks are formed by heat and pressure while buried deep below the Earth’s surface.  Metamorphic rocks may have a banded (striped) appearance or may contain crystals.  Examples: gneiss, slate or marble.  Hint:  metamorphic rocks are never in a liquid state during formation.
  7. Heat from magma can change sedimentary, igneous, or older metamorphic rock into new forms of metamorphic rock.
  8. Pressure from the intense collisions and friction of tectonic plates and pressure also form metamorphic rock.  Again, this pressure can change sedimentary, igneous, or older metamorphic rock into new forms of metamorphic rock.
  9. Igneous rocks are formed when lava or magma harden.  Magma is found below the Earth’s surface and lava is located on the surface.  Igneous rocks are usually found near volcanoes or fissures (breaks in the Earth’s surface).  Examples:  granite, obsidian, or basalt.
  10. When igneous rocks cool rapidly they tend to become glassy and have holes where the gas was trapped.  Slower cooling igneous rocks tend to be colorful and forms large crystals.
  11. Melted materials, caused by an increase in the temperature below the Earth’s surface or caused by the friction between crustal tectonic plates, are one source of igneous rocks.  The cooling and hardening of melted rock determines the type of igneous rocks.  Slow cooling below the Earth’s surface may form granite while fast cooling on the Earth’s surface may form obsidian or basalt.
  12. Illustration of the rock cycle found at <> (You will need to copy and paste the URL in your address bar.)

 Image result for simple rock cycle diagram


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