When students found out that we were going to study rocks for our next science topic, I heard groans from every corner of the room. It turned out that after a preschool fascination with the shiny, round, and sparkly varieties, rocks don’t hold the attention of many elementary students. Changing the perception that “rocks are boring” took a little work, but the resulting excitement was worth it.
Sedimentary, Igneous, and Metamorphic Rock
Because students need to understand both the processes by which rocks form as well as their properties, we first covered the basics: sedimentary rocks form from erosion and weathering of old rocks; igneous rocks begin as magma inside volcanoes; and the metamorphic variety form when rocks are subjected to intense heat and pressure inside the earth.
Sedimentary Rock Activity Using Crayon Shavings
- I broke students into small groups and sent them to stations around the room in which a parent volunteer guided the action.
- At the sedimentary rock station, students shaved wax crayons with a pencil sharpener to represent weathering. When the group had a pile big enough, the wax shavings were moved to a square of wax paper. Moving the shavings represented the second step in the formation process: deposition.
- With their shavings now folded into the wax paper, one member was instructed to compress the packet beneath two hands for ten seconds.
- When the packet was opened—voila!—a sedimentary rock had been born.
The Activity Heats Up With Igneous Rock
- At the igneous rock station, I heated chopped crayons in a microwave while students watched.
- When the wax was melted, students poured part of the wax into a cup of ice water and part into a cup of hot water.
- Students observed the differences produced by these two cooling methods, which represent cooling on the Earth’s surface versus cooling inside the crust.
- Even though there were no crystals to see, the point was made that igneous rocks can cool in two ways.
Metamorphic Rock Experience
The final stop on the rock tour was the metamorphic station.
- Bits of crayons were softened in the microwave, but not completely melted. This represented the heat that rocks are subjected to inside the Earth's crust.
- When they were gooey, students enclosed them in wax paper and were instructed to step on them for two seconds. This, of course, was supposed to represent the pressure inside the Earth.
After stops at all three stations, students compared the rocks they had made. Groups could identify the various original colors in their sedimentary rocks. They recognized the relative brittleness of these “rocks” as well. Likewise, they noted how heating the wax before compressing it made the metamorphic rocks stick together better. Most students commented on the lack of individual colors in the igneous rocks and remembered which cooled fast and which cooled slowly.
We proudly displayed our “rock” collection and referred to it many times during our geology study. This sort of hands-on, process-oriented lesson helps students make connections that stick much longer than a diagram in the book. And I cleaned out my art box! What follows are more rock lesson plans.
Rock Lesson Plans:
Students discover the porous quality of rocks using sandstone.
Students rotate through stations to explore weathering and erosion, key steps in the formation of sedimentary rocks.
Students explore the rock cycle and discuss the fact that it is not a linear process.