Rocks and Minerals > Rock Cycle Activities

Igneous Rocks: Molten Magic

by Deborah Hanuscin

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Concept: Igneous rock formation

Continued rise in temperature can eventually melt any rock until it is molten (called a magma). When the molten rock cools it forms an igneous rock. The size of the grains (crystals) in an igneous rock will depend on the rate of cooling. The faster it cools, the smaller the crystals.

Objective:

Students will be able to describe how igneous rocks form.

Materials:

• goggles
• oven mitt
• powdered sulfur
• tablespoon (metal)
• heat source
• paper cup and plate
• magnifying lens
• water

Procedure:

1. Ask students how igneous rocks form and discuss the process with them.
2. Put on goggles and oven mitt. Slowly heat a tablespoon of powdered sulfur until it becomes a dark red liquid. Pour the melted sulfur onto a paper plate to cool.
3. Take another tablespoon of powdered sulfur and repeat the process. This time, place the melted sulfur into a paper cup of water to cool.
4. After both "rocks" are ready, place them side by side and compare. Use a magnifying lens to examine them closely.

Questions:

1. What can you observe about the rocks you made? How are the rocks similar? How are they different?
2. Break the rocks open and observe with a magnifying lens. Compare what you see.
3. Why do you think the rocks are different?
4. How do igneous rocks form?

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