Just a Bag of Rocks

By Susan M. Frack


Scientists have identified over 2000 different minerals in the earth's crust. 95% of the earth's crust is composed of about a dozen different rock-forming minerals. The rocks composed of these minerals can be formed in three different ways. Scientists can learn many different things about a rock by observing and classifying it.

In this investigation you will become very "friendly" with the rocks in your bag as you group them in different ways.


  • 1 bag of rocks
  • pencil
  • magnifying glass
  • 1 sheet of newspaper  


  1. Cover desk with newspaper.
  2. Spread out your rocks and look them over. Divide them into 3 different groups. Describe your groupings below.
  3. Discuss the groupings with the rest of the class. Listen and share ideas.
  4. Investigate the rocks by  looking at color. Divide the rocks into 3 groups and list below, describing how you grouped the rocks.
  5. Now use the magnifying glass and investigate the rocks. Regroup them into 3 groups and describe below how you grouped them.
  6. Investigate the texture of the rocks. Divide the rocks into 3 groups. Describe your groups below:
  7. Investigate the rocks, looking for layers. Describe your groups below.


  1. Review your lists of rocks for each investigation. Are they the same or different? Explain your answer.
  2. Is it possible to correctly classify a rock by using/looking at only 1 characteristic? Explain your answer.
  3. Which two of the characteristics that you investigated do you feel would be most beneficial to use to correctly identify a rock sample? Explain your answer: