Let's Get Rocks in Our Heads!


This is a culminating activity for a Geology science unit with a goal of recognizing that rocks come in many sizes, shapes, textures, and colors. Successful completion of this task will require the students to:

  • Observe a variety of rocks and record observations (process skills: observing/communicating)
  • Sort rocks according to the multiple properties of color, texture, layering, size, etc. (process skills: (observing and classifying)
  • Record observations in charts and tables (process skills: (communication)
  • Present product/learning to a group (communication)
  • Self-assess success of performing processes and positive group contribution

Prior to doing this activity, read Rocks in His Head by Carol Hurst. In addition, students need to be assigned to bring in 2 to 3 different rocks each to work on this activity. Check student Materials list to see what is needed to complete this task. Student groups can range from 2 to 4 in size.

Student Task

Many people believe that if "you have seen one rock, you have seen them all!" Well, if you believe that, you need to get some rocks in your head because every rock is different! You have just been given a set of rocks that have many differences. Some are smooth and some are very rough. Colors are different. Some are harder and some are softer. These differences are called PROPERTIES. Properties can be divided into two Opposite Characteristics. Size can be divided into the two opposite characteristics of big and small. Some properties are very easy to see, or feel. Other properties are harder to see and you may need to use the magnifying lenses to look closely.


Hot, molten rock, or magma from the earth's interior is the parent material for all rocks. It hardens to form igneous rock. From the time rock is exposed at the surface of the earth, the rock begins to change. In time, the rock formed from the original magma is altered many times. Rocks have different characteristics depending upon their formation. Teachers may have expertise in specific rock classification and are encouraged to share this with students as deemed appropriate. Students should easily classify their rocks in several different ways including: hard vs. soft, shiny vs. dull, smooth vs. rough, single color vs. multicolored, presence or absence of minerals. When testing hardness, discuss how to tell whether or not one rock has actually scratched another. Sometimes the rock you are using to try to scratch another with will actually be softer and leave a powdery trail of itself on the rock being tested. It may look like a scratch. To be sure, try to blow off or dust the "scratch." Hardness is a mineral characteristic. Vocabulary to emphasize during the unit: hard, soft, shiny, dull, smooth, rough, single color, multicolored, crystals, minerals.

Process and Directions

Materials: Your rock collection, crayons, a penny, a magnifying glass, Rock Characteristics Charts (enough for each rock), Student Task Directions (repeated below), Data Sheet, Individual Report , and Self-Assessment .

Step 1. With a crayon, put a number on each rock. Numbers should not be duplicated within your group.

Step 2. Determine Rock Characteristics. To determine whether a rock is hard or soft, scratch each rock using another rock. Try scratching your rock with a penny. Use Student Rocks Chart Worksheet, using information from your Sorting Tree.

Step 3. Complete the following activities:

Student Task Directions

A. Sort your rocks

I. The first property you will use is size:

o On your Sorting Tree, sort your rocks by putting big ones in a one pile, and small ones in another pile. You and your partners have to decide what "big means and what "small" means. When you have grouped the rocks by size, count the number in each group and enter the number on your Data Sheet .

B. Now sort your rocks for other properties:

o Use what you have learned in this unit to explore the following properties

hard, soft, shiny, dull, smooth, rough, single color, multicolored, crystals, minerals.

o Look at the rocks and decide on another property that you can use to form groups. Write the names of the properties in the chart on your Data Sheet .

o Think about the two opposite characteristics you can use to describe the property you wrote on your Data Sheet. Write these on your sheet in the correct column.

o Using your Sorting Tree , put the rocks in piles using those properties. If some rocks do not fit in either group, put them in a third pile.

o Fill in the Data Sheet as you did the first row.

C. Do this over and over again for as many properties and opposite characteristics as you can.

o Remember to write the results on your Data Sheet .

D. Do your Individual Report.

o When you have done as much as you can, tell your teacher you are ready to start your Individual Report.

o Do not complete the Individual Report as a group.


Make enough copies of the following for your class:

Rock Characteristics Charts (enough for each rock)

Student Task Directions

Data Sheet

Individual Report

Classifying Rocks Rubric


Images acquired from:


Teacher: Classifying Rocks Rubric

Data Sheet: The chart on the data sheet should have several properties listed with appropriate opposite conditions. Best groups will fill the entire chart. Properties may be described by phrases (i.e., how they feel, how "holey" it is). The number of rocks in the groups cannot really be evaluated since sample sets varied, and many of the groupings were based on value judgments. However, even though the numbers in both groups may total less than 15, there should never be more than 15 (the total number of samples in each set).

Individual Reports: Students should identify size (big or small), shape (square or triangle), and color or appearance (dark or light, shaded or not shaded), or equivalents, as the three properties. There will, of course, be two objects in each group. Student efforts to transfer the concept of properties with opposite conditions to a grocery store will vary greatly. This is a difficult exercise for this level, and imperfect attempts should be accepted (i.e., "how it feels—hard or soft," "how it's kept—hot or cold"). Some students will have tried to give numbers of objects, as in the previous examples. These can be ignored.

Student: Self-Assessment