Rock Cycle - Rocks (5A)
Pre Lab 

  • Interpreting the different environments in which rocks form.
  • Comparing rock formation with plate tectonics.
  • igneous
  • metamorphic
  • sedimentary
  • none

Students compare the three types of rocks.


Rocks form mainly within the crust of the Earth. Igneous rocks are formed when molten magma formed in the lithosphere cools and crystallizes into solid rock. Magma cools slowly inside the Earth, forming rocks like granite, which have large minerals that can be seen with the naked eye. These are called plutonic igneous rocks. Quick cooling magmas are generally erupted onto the Earth’s surface called volcanic rocks.

Sedimentary rocks are formed only on the surface of the Earth. Sedimentary rocks form at the Earth’s surface in two main ways: (1) from clastic material (pieces of other rocks or fragments of skeletons) which have become cemented together, and (2) by chemical mechanisms including precipitation and evaporation. There are many environments associated with sedimentary rock formation, including oceans, lakes, deserts, rivers, beaches, and glaciers. They may form at all types of plate boundaries, but the thickest sedimentary rock accumulations occur at convergent plate boundaries.

Metamorphic rocks are formed mainly in the lithosphere, wherever there is high pressure and high temperature. If the pressure and temperature are too high, metamorphic rock will melt and become magma. The areas where metamorphic rocks form tend to be very close to those where igneous rocks form.

The key objective of this unit is to emphasize that rock formation can be conceptualized as a very dynamic system called the Rock Cycle. The Rock Cycle is driven by the Plate Tectonic Cycle.

  1. In this exercise, the students locate where rocks are formed within the context of plate tectonics. Review igneous, sedimentary, and metamorphic rocks and their origins. Discuss the various environments where rocks are created. Ask the students to help you fill in the environments that they think might create the three types of rocks.
  2. In the diagram to the left go over which rocks are created. In converging zones, such as subduction, obduction, and collision, metamorphic rocks are always created. However, only in subduction does igneous rock form. Sedimentary rocks will form as the mountains, erode and sediments settle into basins.

    At diverging or rift zones igneous rocks are formed. Sedimentary rocks will form if the area is submerged, like in the mid-Atlantic rift zone. Metamorphic rocks can be formed as the plates move the rocks apart, but it will be only localized. At transform or slip-slide boundaries metamorphic rocks form.

    Sedimentary rocks form as an overlay to all these plate interactions.


[Back to Rock Cycle Grid]   [Back to Rocks (5)]