Rock Cycle - Rocks (6A)

  • Exploring the complexity of the Rock Cycle.
  • Distinguishing where different rock types are located within the Rock Cycle.
  • erosion
  • melt
  • pressure

Students discover where rocks are made in the Rock Cycle.

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Rock Cycle


In many books, the Rock Cycle is oversimplified. Statements like "igneous rocks can become sedimentary and metamorphic;" " sedimentary rocks can become igneous and metamorphic;" or "metamorphic can become sedimentary and igneous" are common.

The Rock cycle is much more complicated. This is illustrated on the Rock Cycle diagram. The large counterclockwise arrows show the general trend of the Rock Cycle. First, igneous rock forms from magma. This rock is then uplifted, weathered, and eroded on the Earth’s surface, forming sedimentary rock. The sedimentary rock is eventually buried within the crust of the Earth, where pressure and temperature finally change it into metamorphic rock. Eventually, some metamorphic rock may melt, beginning the cycle again.

However, the smaller arrow indicate other paths of rock formation. Essentially, any rock type can be melted, weathered, or metamorphosed to make any other rock type. Moreover, a rock can be remade into the same type of rock, i.e., a metamorphic rock can be remetamorphosed. Rock formation is dynamic and very complicated.

The Rock Cycle is tightly interwoven with the Plate Tectonic Cycle, in that most rocks form at plate boundaries. In general, igneous rocks and metamorphic rocks form most abundantly at divergent and convergent plate boundaries. Sedimentary rocks can form anywhere on the Earth’s surface, but the thickest accumulations are associated with convergent plate boundaries, where volcanoes and mountain ranges form. Sedimentary rocks also cover most of the ocean floor.

  1. Go over the Rock Cycle diagram on the student’s worksheet. Fill in the processes like "melt," "erosion," or any other word from the Rock Cycle diagram.
  2. Set up examination specimens of each of the rocks listed below. Write the list of rock types and symbols (below) on the board. Explain the origin and environment of formation of each rock. Be sure to tell the students that these are just some of the places where these rock types can form. Tell the students to locate where each type of rock would form on the plate tectonic diagram. The rock cycle and plate tectonic diagrams  below show the answers. There may be multiple answers for each rock type.

    limestone (L) = sedimentary rock; fine grained, calcium carbonate, formed mainly in oceans, usually with organisms that make shells; fizzes in HCl  (releases carbon dioxide)
    conglomerate (C)
    = sedimentary rock; course grained, formed in rivers
    sandstone (SS)
    = sedimentary rock; medium grained, formed in oceans, lakes, rivers
    marble (M)
    = metamorphic rock; from limestone, formed under increased pressure and temperature
    schist (Sc)
    = metamorphic rock; shiny surface, temperature and pressure; usually formed from basalt and other fine grained volcanic rocks
    gneiss (Gn)
    = metamorphic rock; banded, pressure and temperature; usually formed from granite or other course grained plutonic rocks
    pumice (P)
    = igneous rock; light in weight, volcanic eruption with high percentage of gas; volcanic
    granite (G)
    = igneous rock; large minerals; formed in magma chamber (plutonic rocks)
    obsidian (O)
    = igneous rock; cooled quickly from lava; volcanic rocks
    basalt (B)
    = igneous rock; small, dark colored minerals, volcanic rocks 

  3. You may want students to write a description of each rock on their worksheet.  Use a hand lens to look at the size of the crystals.  Students may also want to draw a picture of the enlarged rock. 

  4. Review the answers with the whole class. Emphasize that the diagram the students have completed shows just some of the possible range of rock-forming environments.

  5. For more information on rocks you may want to read the "Secondary" units on the individual rocks. You may also want to purchase our general Minerals and Rocks Kits for a more detailed explanation.  

[Back to Rock Cycle Grid]   [Back to Rocks (6)]