Edible Igneous Rocks

Rocks are grouped into three different categories based on the way they formed: igneous, sedimentary and metamorphic. We’re going to focus on igneous (pronounced ig-nee-us) rocks, which are formed when molten-hot magma or lava cools way down to air temperature. Before we rock and roll with our experiment, let’s take a look at how it works.

  1. Quick or slow. Depending on how quickly the cooling process occurs, you get lots of different kinds of igneous rocks. Shiny, smooth obsidian rock looks like black glass, because it cools so fast that there’s no time for crystals to form!
  2. Magma versus lava. You’ve likely heard of lava, because that’s what shoots out of volcanoes in an impressive red-hot flow. When that same material is underground, it’s called magma. Rocks can form from magma underground (called intrusive), or from lava above ground (extrusive).
  3. Texture and color. Some igneous rocks are porous and light, like pumice. They’re formed from foaming lava that traps air bubbles inside as it cools. Others are more dense with different colored crystals, like diorite. It’s usually black and white, or sometimes black and pink. There are over 700 types of igneous rocks!

Edible Obsidian Rock

What You’ll Need

  • Ice cubes
  • Chocolate shell topping

What You’ll Do

  1. Kids: Set several ice cubes on a plate. The ice cubes represent the air temperature.
  2. Kids: Pour chocolate topping directly onto the ice cubes. The chocolate represents hot lava — watch what happens when it hits the cold ice cubes. Notice how quickly it “cools” and becomes shiny and hard…obsidian chocolate!

Edible Pumice Rock

What You’ll Need

  • Parchment paper
  • 8"x8" square baking pan
  • Vegetable oil
  • ½ cup sugar
  • ½ cup corn syrup
  • 1 tsp. vanilla or almond extract
  • ½ Tbsp. vinegar
  • Large, deep sauce pan
  • Candy thermometer (optional)\
  • ½ Tbsp. baking soda

What You'll Do:

1. Adults: Tear off two sheets of parchment big enough to cover the bottom and sides of the pan.

2. Kids: Line the square baking pan with parchment, making sure the sides are covered by overlapping the two sheets in a cross formation.

3. Kids: Grease the paper with vegetable oil.

4. Kids: Off heat, add sugar, corn syrup, vanilla or almond extract, and vinegar to a large, deep sauce pan.

5. Adults: Cook the mixture over medium heat, stirring continuously until the sugar dissolves. The mixture will bubble up as it heats.

6. Adults: Continue cooking until candy thermometer registers 300°F, stirring occasionally. If you don’t have a candy thermometer, you can test for the correct temperature by dropping a little of the candy mixture in cold water. Once removed from water, it should separate into hard, brittle threads that break rather than bend.

7. Adults: As soon as it reaches 300°F, remove the mixture from the heat and immediately stir in the baking soda. The mixture will foam.

1. Adults: Tear off two sheets of parchment big enough to cover the bottom and sides of the pan.

2. Kids: Line the square baking pan with parchment, making sure the sides are covered by overlapping the two sheets in a cross formation.

3. Kids: Grease the paper with vegetable oil.

4. Kids: Off heat, add sugar, corn syrup, vanilla or almond extract, and vinegar to a large, deep sauce pan.

5. Adults: Cook the mixture over medium heat, stirring continuously until the sugar dissolves. The mixture will bubble up as it heats.

6. Adults: Continue cooking until candy thermometer registers 300°F, stirring occasionally. If you don’t have a candy thermometer, you can test for the correct temperature by dropping a little of the candy mixture in cold water. Once removed from water, it should separate into hard, brittle threads that break rather than bend.

7. Adults: As soon as it reaches 300°F, remove the mixture from the heat and immediately stir in the baking soda. The mixture will foam.

8. Adults: Pour into parchment-lined pan and allow to cool completely.

9. Kids: Once candy has cooled, use the parchment to pull it out of the pan. Cut or break the candy into bite-size pieces. Store it in an airtight container.

10. Kids + Adults: How does the candy look? Does it resemble pumice rock?

8. Adults: Pour into parchment-lined pan and allow to cool completely.

9. Kids: Once candy has cooled, use the parchment to pull it out of the pan. Cut or break the candy into bite-size pieces. Store it in an airtight container.

10. Kids + Adults: How does the candy look? Does it resemble pumice rock?

Looking for more kid-friendly activities to do at home this summer? Check out our other Adventure Kids Camp activities!