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. How long in advance canthese be made? How long will they last? Thanks

    • Hi Daisy the sugar crystal part will last a very long time if left to fully dry out as it is just sugar. For the chocoalate and fondant check the useby date on your products. 😀

      • Thank you Ann, can’t wait to try this for my granddaughter’s birthday cake.

  2. Colors are endless. This is such a WOW factor on any cake.

  3. I became an instant Ann Reardon fan as soon as I saw this video. The geode was so easy to make. I made a cake at my first opportunity. I am so happy with it. I named my cake. “From Geode, to Gem, to Jewelry”.

  4. Please help me! I started this project yesterday and did exactly what was said. But the sugar hasnt hardened into crystals. It has just become like a lake with ice over the top. Any ideas on how to help me? Please im desprate! I need these for my anniversary!!

  5. Hi Ann,

    Fantastic video! I’m Persian and trying to help my friend with a traditional Persian wedding ceremony(in which they use rock candy with different design)!
    Can I crystallize this rock candy in a heart shape?
    Thanks again…. Absolutely loved this…and will make it regardless for my kids.
    Thank you and Greetings from Texas.

    • Hi Leyia, yes if you make your stick heart shaped then you will be able to make heat shaped ones 😀

  6. i always thought this idea was really cool, so i decided to try it out without coloring or flavoring, but it only formed a small amount of tiny crystals on the top. but now i read that you can take small sugar crystals and drop them to the bottom to ‘seed’ them, but could i use regular suger to do that?

    • hi maxime you could try that but it may just cause all the sugar to crystalize out too quickly

  7. These are amazing! I love the chocolate ones my family doesn’t seem to like the fondant lol 🙂 thanks for sharing this!

  8. I really love this recipe & just made the sugar solution. Do you put it in the fridge to cool or do you just leave it out for 48 hours? Thanks!

  9. Hi,
    I just made your Rock Candy Geode Recipe and I hope it turns out good. 🙂 I may have accidentally turned the sugar solution into a syrup too. But, it is forming some crystals more along the top. I will just leave it for longer and I hope the crystals form. I love your videos. <3

    • hi Ashlee, if the crystals form on top you could try breaking them off and letting them sink to the bottom, more crystals should form on them

  10. Hi Ann,

    I was really impressed with this recipe and I knew I had to make it for my birthday, as I love rocks and baking, so this would be a perfect way to unite my two hobbies!

    Unfortunately, my first attempt with the chocolate method didn’t work at all. Only a couple of crystals had formed after three days. Is it because I greased the foil (I wasn’t sure if you were supposed to, or only for the fondant method)? Or is it because I overcooked the sugar solution as you mentioned previously?


    • Hi Eva, you do not need to grease the foil. There are many factors involved in how long it takes for the crystals to form including the temperature and humidity of where you live. To speed it up you could try adding more sugar to the original solution, and make sure it is not a syrup.

      • Hi Ann,

        Thanks so much for your reply. I tried again with cooking it for less time and using the fondant method instead, and it worked really well! I added an icing rock hammer and chocolate covered marshmallows for “rocks” and my cake turned out like this:

        • that’s awesome Eva great job and thanks for sharing a pic 😀

  11. Hi Ann,

    Great site, I love these geodes and have made them often for little gifts people, I was thinking of getting some Lustre Dust and adding a little to the mix too to make it really pop!

    I have not used Lustre Dust before, any ideas if this would work or am I heading for disaster?

    • Hi Benji-man, I’d try dusting it on the top rather than mixing it in.

  12. would adding flavoring (alcohol based or candy melt flavoring) to the sugar syrup (or fondant) ruin the whole chemistry of this? I think having flavored geodes would be so much better. I just don’t know if it’ll work.

    • Hi Amy, yes it still works, I made strawberry ones.

  13. Dear Ann,

    First of all, I hope you’ll understand my e-mail. I’m from Holland, and English isn’t a language I practice on a daily basis. (yes, you have viewers all over the world!)

    I’ve tried to make your rock candy, but if failed. I made the one, you have to cover in chocolate. My first attempt I put 3 times more sugar than water in a pan. Cooked as you showed in the video. After 2 days of resting it broke into pieces. I tried again (reheating it and ad some more sugar and water) But then it wouldn’t crystallize. I only get a thin layer on top of the sugarsyrop.

    Help me, what am I doing wrong?

    I’m really glad I found you page. My sons and I really enjoy baking all sorts of cakes and cupcakes. My oldest son loves the Mickey Mouse cupcakes. I induce astonishment with my family with that recipe.

    Greeting from the other site of the world!

    • Hi Mariska, Your English is good 🙂
      If the crystals are not forming at all then the sugar has been over heated to form a syrup rather than a super-saturated solution of dissolved sugar. The one that broke sounds like it was too thin, is that what you mean? In that case just leave for longer for crystals to form, once thick tip upside down to drain and dry out.

      • Hello Ann,

        Thanks for your comments! How long does the sugar syrup needs to boil? I thought I boiled it for a few moments, just like in you video. Until I didn’t saw any sugar in the water.

        I will retry soon ans let you know if its works.


        • Hi Mariska, the videos are edited down to make them concise, boil just until the sugar is dissolved then remove from the heat immediately.

  14. Hey Ann,

    I’ve tried the chocolate one two days ago and I’ve got a problem.
    The crystals grew at the surface and not at the ground! Now I have an 2 mm thick crystal area. But not in geotide form -.-

    By the way, you’ve done a great job with your website and your channel!

    Many greetings from Germany

    • Hi Matthias, Your crystals are being tricky! All I can suggest is try breaking of any that form on top and pushing to the bottom next time to encourage them to grow at the base.

  15. I thought this idea was so cool, so last night I tried it, making a few different colors and flavors. This morning I uncovered and checked on them (I’m doing the chocolate method) and a noticed that a sort of shell of hard flat sugar formed on the surface of the solution. it only formed on some of them.. could this be because of the different flavoring a I used? is this normal? should I remove the shell? I’d appreciate if you could answer my question, thank you 🙂 I love your blog and videos!

    • Hi Amanda, yes that does happen sometimes and yes you can just remove it from the surface.

      • This is happening to mine right now. It’s a thin crust on top. I kind of broke it up with a toothpick and tried to sink them down so that crystals can form on them. Do you think I ruined them by doing that? They still have another day to sit.

  16. Hello Ann,
    I just wanted to show you how my wonderful geodes came out. thank you so much. my niece will love these on her cake.

    • Hi Ruchelle, the blue one is so pretty, great job, hope your niece had a great birthday.

    • This was this finish product. thank you Ann for helping me make the perfect geode cake for my niece she loved it.

      • They look great I am glad your niece loved it

  17. I really loved how this came out and I will definately be making more in different colors. Thank you Ann. **cheryl**

    • Thanks for sharing a pic Cheryl Hope you have a great week this week 🙂

  18. hey would this be good for a science fair project ann ?

    • Hi dangelo, we don’t have science fairs here, do you mean would it be good for a whole class activity?

  19. I love this recipe, but It didn’t work for me.
    I tryed to make the second method, but it never crystallized (I left it for 2 weeks), the rare was that yesterday I put the same sauce in a fondant and it works.
    I really want to do it with chocolate, do you have any recomendation?

    • Hi Aida, yes you could take some crystals off you fondant one and drop them into the plain one to ‘seed’ it. Mine did not need that it just crystalised on its own but that should fix it if it is not starting for you.

  20. Love this!! My 7-yr-old is obsessed with rocks and wants to be a geologist someday. This will be a perfect decoration for his Minecraft birthday cake next month! Thanks so much for sharing, brilliant!

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