Homegrown Science: Rock Candy Geodes
Here’s a sweet lesson for keiki. Watch crystals grow in an incredible edible geode.
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
- Bowls of various sizes (each will form a geode)
- Wooden spoon
- Butter knife or spoon for spreading
Sugar Dome Instructions:
- Line inside of a bowl with a sheet of foil large enough to fold over the rim of the bowl.
- Pour the water and sugar into a pot.
- Heat the mixture on high until it begins to boil, stirring occasionally until sugar dissolves. The mixture should be clear.
- Wait a few seconds until the bubbles settle.
- Add a few drops of neon food coloring. Stir until color is incorporated.
- Pour mixture into the foil-lined bowl.
- Leave the bowl in a cool, undisturbed spot away from direct sunlight for at least seven days. The bottom of the mixture will crystalize.
- Once crystals form, slowly drain leftover liquid from the bowl. Crystallized sugar should sit at the bottom of the foil.
- Gently peel off the foil to reveal a sugar dome. Be careful not to crack it. Set aside on a sturdy surface.
- Melt white chocolate candies in a pot or microwave, according to instructions on the package.
- Using a spoon or butter knife, spread the melted candies on the outside of the sugar dome, covering it completely.
- While waiting for white chocolate to harden, melt the dark chocolate candies.
- Cover the dome with dark chocolate.
- (Optional) Sprinkle cacao powder in between and around the layers for the “dirt effect.”
- Let dry for 30 minutes.
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- 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.