Ann Reardon

Rock Candy Geodes Recipe

how to make rock candy

Geodes are beautiful so let’s make them delicious too. Follow the step by step instructions to make fondant or chocolate rock candy geodes. You can give them as a gift on their own or use them in cake decorating.

Fondant shell
350g (12.35 ounces) fondant
black and brown coloring

Using aluminum foil make a bowl into a rock shape and line with another sheet of aluminium foil.
Marble some grey, black and brown shades of fondant as shown in the video and roll it out.
Roll out some white fondant and place over the top of the coloured fondant.
Place the fondant (rock colour down) over the aluminium foil bowl. You can leave this to dry out or use immediately.

Supersaturated sugar solution recipe

3 cups or 640g (22.58 ounces) sugar
1 cup or 230ml water
few drops of food coloring
few drops flavoring

Heat the sugar and water in the saucepan and stir until completely dissolved. Remove from the heat.
Allow supersaturated sugar solution to cool slightly and then pour into the fondant shell. Leave overnight for crystals to form.
Remove any excess crystals that have formed in the middle, turn upside down and leave to dry out.
Using a sharp knife, trim off excess fondant around the level of the sugar crystals.

Chocolate Shell

how to make rock candy

300g (10.58 ounces) white chocolate melts or candy melts
2 Tbsp or 14g (0.49 ounces) cocoa powder

Make an alfoil bowl as shown in the video and pour in the hot sugar solution, completely wrap in alfoil and leave for 48 hours for crystals to form. Tip off excess sugar solution, peel off alfoil and leave upside down to drain.
Melt some candy melts or white chocoalte melts and pour over the back of the candy shell. Once set add some cocoa powder to the remaining melts and pour over the top of the white chocolate. Trim to the edges of the crystals.

rock candy recipe

by Ann Reardon How To Cook That

My Cookbook

ann reardon crazy sweet creations cookbook
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All recipe quantities in the book are in grams, ounces and cups.

182 Comments View Comments

  1. does castor sugar work better than granulated sugar?

    • Yes definitely!

  2. This is really cool idea, I tried the chocolate shell and left the sugar syrup in a bowl just like the video for 48 hours and very little crystallization, not much. What went wrong with me? and why is the flour needed in the bowl, I did it just like the video. Maybe need to leave more time ?

    • Well I left the sugar syrup for 5 days and was able finish my geode candy. See pictures, it came out pretty cool, now I will make another one maybe leave it for a longer time.

      • Looks great Hector.

    • Maybe it wasnt enough sugar. I made a few for my sisters birthday as well, and they didnt really set, so i put them in the freezer, after I let them dry for 6 days. They werent perfect, but looked good, because they broke into small pieces

  3. Hi Ann, I tried this yesterday but it didn’t quite work! I used the fondant method. When I checked it this morning the sugar had set completely! There was no liquid to pour off, just a lump of sugar. Any ideas?

    • Wow, people usually have the opposite problem. It is difficult to assist without actually seeing your results but there may be two things that can help. Be really careful to ensure all the sugar is dissolved in the syrup. Don’t leave any grains on the side of the pan or bottom of the pan or it will quickly crystalize out. That is what it seems like it might of happened in your case. If you dont think that was the issue, then try a slightly less concentrated sugar solution and see how that goes.

      • Thank you for your reply. I did wonder if I’d overcooked the sugar solution. I’ll follow your advice and try again!

  4. Wow! Now this is just what I’ve been looking for, a recipe that doesn’t require a diploma from the Institute of Culinary Education!
    A treat fit for this RockHound!
    Thank you!

  5. Thank you so much for sharing! It was very easy to follow! My son is going to be so excited when he sees his birthday cake!

    • Wow Nora, That cake looks amazing. The Geodes look phenomenal!

    • Nora, that’s incredible!

  6. Ann; Thank you so very much for sharing this amazing idea. Made this for my niece, I’m sure she will love it. Had some trouble getting my first two batches to crystallize, but after udjusting the solution from 3-1 to 4-1 the crystals formed rapidly. Thank you agin for this, and all your great videos. I’m a big fan.

    • Hi Alec, This looks amazing! Great problem solving too!

  7. Is it normal sugar used ?

    • Hi Danielle, It is best to use white castor sugar (also known as caster or superfine sugar).

  8. Well, this is what I got. Not bad for the first time trying, right? ??

    • Hi Sara, Have you pulled your geode apart? If it broke you can heat isomalt and use it to stick the pieces together.

  9. This only worked for me in I threw a hard candy (lifesavers work well) into the bowl so that the crystals had something to grow on. Then it works great every time. I made large ones and small ones in cupcake pan slots.

    • Great hint Anne!

  10. Can you make these ahead and how would you store them?

    • I put some in a display case at school and they look great over a year later. I don’t think I would eat though.

    • Hi Veronica, you can store them in an airtight container in a cool place. They should keep for a week or two.

      • Hello, i’m very sad that mine did not work, my chocolate burned and i did it the way you did, my crystals melted and now its just a big pile of nothing. I am looking for another way to do crystals on the web. I really needed this to be done by Thursday….and now it’s not… 🙁 🙁 🙁



        • Hi Lisa, Oh dear, I wonder what went wrong. From your comment we can’t identify the problem. The crystals wouldn’t melt if set properly unless exposed to heatIf you are desperate for some crystals for a project, a quick alternative is to use the rock candy crystals sticks. Break the crystals off the sticks and heat a bit of isomalt and use it to glue the crystals together and place on your chocolate.

  11. Hello, Ann! I’ve tried to make this sugar geode and it didn’t work for me. I’ve followed all recipe, but no crystals were formed next day. What did I do wrong? Thanks a lot!

    • Hi Beatriz, It si hard to tell without seeing what you did but you can speed up the process or help it along, by ‘seeding’. Drop in a couple of pieces of crushed or broken sugar candy or similar to encourage the crystals to grow.

  12. Can I use tempered chocolate instead of candy melts?

    • Hi Aniko, Yes you can but you may find the melts easier to work with.

      • So finally, here are mine! It’s a bit tricky to get them right but it’s well worth the effort, thanks for the great idea Ann! Not a great pic but it does not let me upload multiple ones so I had to combine them. I’m planning to put these on a mirror glaze cake. Will share a pic of that, as well if it works out 🙂

        • …and here it is 🙂

          • So impressive Aniko! One of the best I have seen!

          • What did you do? I want to teach my students how to do this. I am a teacher for students that would enjoy this project, recipe wonderful art piece. They give me inspiration to put it into my Science lesson and make it multidisciplinary and use as art and culinary. Please tell me how to get through the tricky parts of making it turn out okay?

            Urs looks fantastic!

            Teacher in California

          • Wow~!

          • Susan: If this was a question for me, if you follow the instructions carefully in Ann’s recipe it should work (it did work for me at least). I’m not an expert but from my experience, the trickiest bit is to wait long enough till the sugar is completely dissolved before removing it from the heat but at the same time making sure its not overcooked and turned into sugar syrup. I also sprinkled some sugar on the aluminum foil before pouring in the hot solution to kick start the crystal formation at the bottom of the bowl. I did check on them after 48 hours and removed the sugar crust forming on top but I figured the geodes were not thick enough so I let them sit for another 2-3 days before removing them from the foil. Instead of candy melts I used tempered chocolate but it should not really make a difference. I hope this helps. Good luck with the science project 🙂

          • That is gorgeous! For the cake, I assume it’s covered with a fondant that has the purple mixed in but not totally to give that swirled look of a polished stone. What gives it the high shine look?

        • This is absolutely breathtaking!

        • Fantastic work Aniko!

          • Thank you! :)))

  13. lovely tutorial Ann , am going to try this for my husband’s birthday next month . . Only one question , in the attached pic how do you get a hole in the middle of the geode. TIA

    • Hi Shama, The geode in this picture is not made via the method Ann uses. In fact the sugar crystals are not grown in this shape. They have used the rock candy/candy sticks. The crystals are removed from the sticks. Roughly chopped Chocolate is spread in the circle shape and melted chocolate poured over and the crystals sprinkled in to look like a geode. Once set, the shape is turned over and process repeated on the other side.

      • Thanks for the explanation , Will try Ann’s recipe first as it looks more simple .

  14. I m trying it right now… For my brothers birthday. i m so excited 😀

  15. This is a really interesting and fun recipes for familes

  16. Hi Ann,
    This is the result 🙂 it turned out nice although I used cane sugar. Thanks for your advise to use food flavouring, it tased very sweet but good 😉

    • Hi Rosalie, they look great. Well done!

  17. Hi! this looks wonderful and id like to use your recipe. can you tell me how to assemble this to appear in a cake? thanks.

    • Hi Amanda, There are lots of options for this and some bakers make incredible frosted cakes with geodes embedded in the side with. A quick search online should give you heaps of ideas as to what is possible. A simple option is to position them on top of a cake. You could make the surface of a cake look like rocks and dirt using crushed biscuits.

  18. Hi!
    I’m planning to make a chocolade geode. I was thinking of putting some lemon juise or orange juise to the sugarkristals to give it some flavour. Is it a good idea?

    • Hi Rosalie S, adding any acid will prevent the sugar from crystallizing and as citric juices are acidic they will work against the process. You would be better to use a commercial flavour if desired.

      • Ok, thank you for your reply. I have started to make the geodes and for the sugar solution I used some commercial flavouring, food coloring and cane sugar. Will the cane sugar form crystals just like regular white sugar?

  19. thank you so much for this recipe . so much fun

  20. plain sugar geode

    • Great work Gali!

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