Rocks and Minerals > Rock Cycle Activities

Igneous Rocks: Igneous Mint Fudge

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. All three main types of rock (igneous, sedimentary, and metamorphic) can be melted to form magma.

Objective:

Students will be able to explain how igneous rocks form.

Materials:

• water
• 4 cups sugar
• 1¾ cups evaporated milk
• 1½ cups butter
• 12 oz package of chocolate mint wafers
• 16 oz package of marshmallows
• stove
• candy thermometer
• heavy, high-sided sauce pan
• measuring cups
• 13" x 9" x 2" pan
• butter (for greasing pan)

Directions: Butter the sides of the saucepan. Combine milk, sugar, and butter and stir until the sugar is dissolved and the mixture boils. Place candy thermometer into mixture and cook to soft ball stage (243° to 236° F). Remove from heat, then add mint wafers and marshmallows. Stir until blended. Pour immediately into a buttered 13" x 9" x 2" pan. Cut when cool and firm.

Procedure:

1. Prepare the fudge ahead of time according to the directions. Save an extra wafer and marshmallow to show students.
2. Ask students how igneous rocks form. (They are the result of magma, or molten rock, which has cooled.)
3. Show students the ingredients for the igneous rock fudge (marshmallow, wafers, etc.). Ask them to write their observations about these "rocks" in their science journals.
4. Pass out pieces of igneous rock fudge. Ask students to record their observations about these "rocks" in their science journals. You may wish for them to answer the questions below.

Questions:

1. How are the first "rocks" you were shown like the second?
2. How are they different?
3. What made the rocks change?
4. How do igneous rocks form?

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