Rock Cycle - Rocks (2)
Pre Lab 

   
OBJECTIVES:
  • Recognizing the three types of rocks.
  • Comparing characteristics of different types of rocks.
VOCABULARY:
  • igneous
  • lithosphere
  • metamorphic
  • mineral
  • rocks
  • sedimentary
MATERIALS:

Students color a worksheet in order to learn where rocks form.


The Sierra Nevada Mountains, California

BACKGROUND:

Igneous rocks come in many varieties. However, all igneous rocks began as molten rock (magma) which cooled and crystallized into minerals. Igneous rocks may look different because of two factors: (1) they may have cooled at different rates and (2) the "mother" magma (original melted rock) was of a different composition. Variations in these two factors have created many different types of igneous rocks. When the magma cools at different rates, it creates different sized minerals. Quick cooling magmas have small minerals (with the exception of obsidian, which is actually composed of silica, but has no crystalline structure). Basalt, for example, has small minerals, most of which can only be seen under a microscope. Magma that cools slowly creates rocks like granite which have large minerals that can be seen with the naked eye. Geologists classify igneous rocks based on both their crystal size and composition. The Rock Cycle has its origin in Igneous Rocks.

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. Sedimentary rocks are usually associated with liquid water (which facilitates erosion, transportation, deposition, and cementation). However, sedimentary rocks may also form in dry, desert environments or in association with glaciers.

Metamorphic rocks are igneous, sedimentary, or preexisting metamorphic rocks that have been changed by great pressures and temperatures within the crust and upper mantle of the Earth. The temperatures were not enough to melt the rock, otherwise, an igneous rock would have formed. The pressures were much greater than those required to simply break the rocks into pieces. They were high enough to change the chemical make up of the rock by forcing the elements in it to "exchange partners."

All three types of rock make up the Earth’s lithosphere, the outermost layer. The lithosphere averages about 100 kilometers in thickness. It is like an eggshell compared to the Earth’s total radius (the distance from the Earth’s core to the surface). The lithosphere is solid rock. Sedimentary rocks are the most abundant rock only on the surface of the Earth, but igneous and metamorphic are abundant deeper into the mantle.

PROCEDURE:
  1. Introduce the students to the lithosphere. Ask them where most of the rocks that we see on the surface of the Earth were created. Explain why the lithosphere is the correct answer. Show them a cross-section of the Earth by showing them the physiographic relief globe. They will be amazed at how thin the lithosphere is compared to the rest of the Earth. Explain that igneous, sedimentary, and metamorphic rocks are created in the lithosphere. Briefly distinguish between the lithosphere, hydrosphere, and the atmosphere. Lithosphere is sphere of rocks; hydrosphere is sphere of water; and atmosphere is Earth’s envelope of gases.


 

  1. Write the following on the board:

    IGNEOUS ROCK = hot rocks or melted rocks (ask students to think of hot areas) are found:
      

    • volcanoes

    • inside the Earth (not near the center, more toward the outside, within the crust)

    SEDIMENTARY ROCKS = cool, wet, or fossil rocks (ask students to think of water) are found:
      

    • rivers

    • oceans

    • lakes

    METAMORPHIC ROCK = changed, squished, or "rhinestone" rocks (ask students to think of squishing) are found:
      

    • inside the Earth (not near the center, within the lithosphere and upper mantle)
       

  2. Give students the worksheet and color the appropriate rock types. Make sure students understand how to use a map legend.

  [Dictionary]  
[Back to Rock Cycle Grid]   [Back to Rocks (2)]