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Rock Candy Geodes

If there’s anything better than cracking open a seemingly plain stone and finding it lined with crystals inside, maybe it’s making a geode, in the kitchen, with your kids. And using sugar to do it.

A rock candy geode makes an especially great talking point if kids are curious about geology. You can go deep on how volcanic action forms real geodes, and watch oddly satisfying videos of people cracking them open. But the sweet kitchen techniques involved offer cool lessons on their own.

While cooking all of the rock candy that’s used to make the geodes doesn’t take much time, there is a bit of a wait until the final product can be unveiled—but trust us, it will be worth it. There’s plenty of work for little hands to help out with here, from making a mold to give the sugar its rock-like shape to mixing and coloring (and flavoring!) the various layers of sugar for the rock candy. There is some boiling of candy syrup, too: Just be mindful of the possibility of hot-liquid splashes.

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Ingredients:

For the mold
  • Small bowl
  • Tinfoil
  • Cooking spray or neutral oil, for greasing
For the rock candy
  • ½ cup brown sugar
  • ½ cup white sugar
  • 3 cups white sugar (measured separately)
  • 1 ½ cups water
  • Food coloring
  • Vanilla or other flavor extract (optional)

Steps:

  1. Step 1

    To make the mold, tear a sheet of tinfoil into strips and roll them into a variety of shapes and sizes—balls, sausages, crinkly misshapen lumps. Make enough to fill in the bottom third or so of the bowl you are using, and then layer over them with a full sheet of tinfoil, pushing it down into the various crevices between the balled-up pieces. This will provide the texture and topography for the rocky outside of your sugar geode. Coat the tinfoil with cooking spray, or run with oil to make it easier to remove the rock candy.

  2. Step 2

    To make the rock candy, mix ½ cup of brown sugar with 4 tablespoons of water in a heavy-bottomed saucepan. Stir, mixing the water into the sugar until it is evenly moist.

  3. Step 3

    Place the pan over high heat and cook until the sugar melts. As soon as the mixture begins to bubble, pull it off of the heat, and dump the syrup into the geode mold. Tilt the mold back and forth and side to side, allowing the syrup to flow into all of the cracks in the tinfoil. Set aside to cool and harden.

  4. Step 4

    Next, make the white layer of rock candy, which will sit between the brown sugar stone and the hued crystals of the geode’s interior. Mix ½ cup of white sugar with 4 tablespoons of water in a heavy-bottomed saucepan, and cook the mixture just as you did the brown sugar. Allow the syrup to cool before pouring it into the mold, so as not to melt your previous layer.

  5. Step 5

    Finally, make the colored (and flavored, if you’d like) crystal layer—the inside of the geode. Combine 1 cup of water with the 3 additional cups of white sugar, and boil until the sugar is completely dissolved. Add food coloring to achieve your desired hue and a few drops of flavor extract (if using). Allow the mixture to cool, then pour over the other sugar layers.

  6. Step 6

    Cover the bowl with a clean towel and set aside for 24 to 48 hours, or until crystals have formed and the middle of the geode has hardened. When the rock is finished there will still be some liquid in the center, which should be dumped out. The rock candy can be carefully removed from the mold and set aside for another day or so to dry completely. After that, kids can finally play with—and eat!—their fresh geodes.