Rock Crystal Cycle

Rocks are made up of minerals mixed together. These minerals have many different crystalline shapes. This project involves children in creating several different crystal types so they can observe the variations.

There are many different mineral types that can be made at home or in the classroom. The ingredients used here are non-toxic examples that will not hurt children if ingested or exposed to the skin. The second floor of The Field Museum has a display of the crystal shapes and some minerals we use in everyday life such as fluoride for better teeth and the hardest known mineral, diamond.

Getting Our Hands Dirty

Plan it!

  • If you're planning to make multiple crystals, set up the different dry ingredients into stations, with different food coloring at each station.
  • This experiment will work best with hot or boiling water, but make sure to use glass containers (not plastic) if the water is very hot or boiling.
  • If you're using scientific instruments, 1 tbsp = 15mL.

Do it!

  • Place the dry ingredients into labeled cups and add water and food coloring to each cup according to the following chart:
    Baking Soda Salt Sugar Epsom Salt
    1 tbsp. baking soda 5 tbsp. salt 12 tbsp. sugar 5 tbsp. Epsom salt
    ½ cup hot water 6 tbsp. hot water 5 tbsp. hot water 6 tbsp. hot water
    2 drops food coloring 2 drops food coloring 2 drops food coloring 2 drops food coloring
  • Stir each solution until all of the dry ingredients are mixed. Slowly add a little more of the dry ingredient until there is just a little bit that does not dissolve. This means the mixture is "saturated" and it is ready to make crystals. It may take a long time to dissolve some of the salts, but keep stirring.
  • Put the cups in a protected area and let all of the water evaporate. This process can take about a week. You can check the containers each day to see if small crystals are starting to form.
  • When the crystals are dry you can take them out of the cups and display them! But be careful, because some of these crystals are very fragile.

Thinking About It

  • Compare the different types of crystals you made. How are their shapes different? What do you think causes these different shapes? Did some ingredients form crystals faster than others?
  • Collect a sample of rocks from your yard or street. With adult supervision, crack some of the rocks and see if they have any crystals inside.

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