Homegrown Science: Rock Candy Geodes

Here’s a sweet lesson for keiki. Watch crystals grow in an incredible edible geode.


Photos: Nicole Ladonne Blair

The Science

Excessive amounts of sugar mixed with water create a supersaturated solution. When heated, molecules in the solution collide and stick to one another. This crystallization process is called nucleation.


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  • 2 cups white sugar
  • 6 cups water
  • Neon food coloring
  • 1 package each of white and dark chocolate melts
  • Cacao powder (optional)


  • Measuring cups
  • Foil
  • Bowls of various sizes (each will form a geode)
  • Wooden spoon
  • Pot
  • Butter knife or spoon for spreading


Sugar Dome Instructions:

  1. Line inside of a bowl with a sheet of foil large enough to fold over the rim of the bowl.
  2. Pour the water and sugar into a pot.
  3. Heat the mixture on high until it begins to boil, stirring occasionally until sugar dissolves. The mixture should be clear.
  4. Wait a few seconds until the bubbles settle.
  5. Add a few drops of neon food coloring. Stir until color is incorporated.
  6. Pour mixture into the foil-lined bowl.
  7. Leave the bowl in a cool, undisturbed spot away from direct sunlight for at least seven days. The bottom of the mixture will crystalize.


Coating Instructions:

  1. Once crystals form, slowly drain leftover liquid from the bowl. Crystallized sugar should sit at the bottom of the foil.
  2. Gently peel off the foil to reveal a sugar dome. Be careful not to crack it. Set aside on a sturdy surface.
  3. Melt white chocolate candies in a pot or microwave, according to instructions on the package.
  4. Using a spoon or butter knife, spread the melted candies on the outside of the sugar dome, covering it completely.
  5. While waiting for white chocolate to harden, melt the dark chocolate candies.
  6. Cover the dome with dark chocolate.
  7. (Optional) Sprinkle cacao powder in between and around the layers for the “dirt effect.”
  8. Let dry for 30 minutes.


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Our Tips

  • The boiled sugar-water will be extremely hot and dangerous to handle. An adult should supervise children.
  • For foil, we recommend heavy-duty nonstick Reynolds Wrap.
  • The chocolate coating and foil base do not have to be smooth and perfect. Aim for a lumpy, bumpy texture resembling “rock geodes.”
  • Crystallization may take up to 10 days or more in Hawai‘i’s humid climate.