Learning about how igneous rocks form is fun and easy with an edible igneous rock activity. Igneous rocks are one of three types of rocks along with sedimentary rocks and metamorphic rocks.
Learning about Igneous Rocks
Igneous rocks form when molten rock cools quickly. This often occurs near volcanoes. When the magma (molten rock under ground) rises to the surface, it is called lava. When the lava cools it forms igneous rock. There are different types of igneous rocks based on what the rock is made of and how quickly it cools. Purchase a set of igneous rocks like the one below to help study the different types.
My favorite types are obsidian and pumice. Obsidian is black, shiny, and smooth. It forms when lava cools quickly. Pumice is usually less dense than water. You can visually see the holes within the rock. The magma froths and contains lots of air bubbles. Then, it is ejected out of the volcano. The rock cools quickly around the gas bubbles and the holes form where the gas bubbles were.
Read more about igneous rocks in the following book.
How to Make Easy Edible Igneous Rocks with Magic Shell Chocolate
The simplest way to show how a rock forms is to let kids watch chocolate cool. Dealing with hot chocolate is not the safest activity for kids. That’s where the Magic Shell chocolate ice cream topping comes in. You don’t need to heat it up. The chocolate topping has coconut oil in it so it hardens when cooled.
Pour the topping on an ice cube. It will be liquid as it comes out. This represents lava flowing out of a volcano.
As the chocolate cools, it will harden. This represents an igneous rock. My son wanted it to be obsidian.
Edible Igneous Rock – Sponge Candy Recipe (aka Honeycomb or Sea Foam Candy)
Another fun way to talk about how igneous rocks form is through making sponge candy (or honeycomb). The use of baking soda in the recipe causes bubbles to form in the candy. When the candy cools, you are left with holes – just like pumice rock.
Ingredients to Make Sponge Candy
- 1/2 cup sugar
- 1/2 cup corn syrup – golden syrup in the UK
- 1/2 tablespoon vinegar
- 1/2 tablespoon baking soda – Bicarbonate of Soda UK
- 1 teaspoon vanilla or other flavoring
Instructions for Making Sponge Candy
Line the bottom and sides of an 8×8 square pan with parchment paper and grease with vegetable oil. Add sugar, corn syrup, and vinegar to a large, deep sauce pan. (The mixture will bubble up.) Cook over medium heat stirring continuously until the sugar dissolves. Continue cooking until candy thermometer reads 300°F. Be patient. It will take a while. Stir occasionally. As soon as it reaches 300°F, remove from heat and stir in the baking soda. The mixture will foam. Pour into parchment lined pan and allow to cool completely. Once candy has cooled, use parchment paper to pull it out of the pan. Cut or break the candy into bite sized pieces. Observe the spongelike appearance of the candy. Discuss how it resembles pumice rock.
More Rock Activities for Kids
- Make edible sedimentary rocks to learn about how sedimentary rocks form.
- Read these tips for getting started rock collecting with kids.
- When talking about igneous rocks, you’re bound to make a volcano. Try one of these 10 ways to make a volcano with kids.
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