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. Rating: 5

    I was reading the comments an noticed someone mentioned that castor sugar was necessary, but I did not see it specifically called for in the recipe. Is it used for making the rock candy?

  2. […] 41. Rock Candy Geodes from How to Cook That (We tried it too!) […]

  3. Rating: 4.5

    This was amazing, thanks for this!
    The only problem I ended up with making the fondant version was it split and lost its shape and broke the candy when taking it out.

    Will I solve this by leaving the shell to dry out before pouring in the candy?

  4. Rating: 5

    Can I just make
    The gseod without any shell at all?

  5. Rating: 4.5

    I tried it out, and the entire thing hardened into a rock-solid coloured piece of sugar. I want to try again, but I am not sure what I did wrong there. Any tips?

  6. Rating: 5

    Hello, and may I say that for one youtube’s algorithm was right – although I never even googled any cooking channels preferring to improvise, one day it suggested me yours, and your lovely cooking corner rocketed up into my favourite one on the platform! I do love making sweets to give away to people, and you have so many nifty tips to provide. I love it, and I thank you so much for making the most amazing channel there is. I cannot wait to try out all those ideas you provided.
    And thank you for the recipe! I really wanted to try a party candy like this, and today was my chance to. Never worked with sugar like that (I am more of dough, mousse, meringue, pudding, custard and all things creme kind of cook – I don’t even work with chocolate that much), so I have a question!
    I kind of made one pan of sugar solution, and separated it evenly into another pan when dissolved, because I wanted to try and make one with a few drops of mint essence, and one – without. While I was working with my first batch, the second started cooling down a bit too fast, and stated turning into this sort of fudge on top. Just curious, I took a few spoons out to watch how it goes, and soon it created this clay-like fudge. I am not sure if that is one of the essential processes for crystallisation to begin or if I did something wrong and should throw that out and try again. Can anyone tip me on this?

    Also, just out of curiosity: I am making chocolate shell, so my first try on sugar crystals lies tightly wrapped in the kitchen… I was wondering, why wrapping in a towel is needed? And why it takes twice as long as being crystallised on a fondant.

    • Hi Valentine, I’m so glad you found the channel. It is a supersaturated sugar solution so if it is going like fudge on top the sugar is crystallising back out immediately. This can happen if there is some sugar or anything small that causes it to crystallise back out or even if you over stir it. Wrapping it int he towel allows it to cool down more slowly encouraging bigger crystals instead of tiny ones.
      I also have a new post with an easier way to make geodes here

  7. Rating: 5

    Hi Ann,
    Firstly I would like to say that I love your channel and enjoy it very much!
    I appreciate the honest and accurate explanations you give.
    I attempted to make the Geode cake as you instructed in the video (which I watched at least 10 times).
    I guess attempted to make them bigger than what you show on the video, because it took them about 1 week to form nicely.
    Since they were not ready in time for the cake, I took your idea of the fondant covered by chocolate, and glued coloured sugar with some coloured white chocolate to the fondant.
    I was very pleased with the result, as this was the first time I attempted such a cake.
    Thanks and keep up the good work 🙂

  8. Rating: 4.5

    Has anyone tried to use plastic Easter eggs as molds for the aluminum foil forms? Then after crystals form, put them together and then cover the egg shape with the fondant?

    • g’day tom, you could line and Easter egg mold with fondant, then grow the crystals the centre, once it is dried out remove it from the mold and cover in chocolate. The only tricky part might be getting it out of the mold without breaking.

  9. I made this for my brother and he loves it. Would recommend

    • Awesome thanks for the photo JWall ?

  10. Hi, Thanks for sharing this video. I made these last week for a geology professor’s retirement party and they were a big hit! I shaped the fondant shells in a mini muffin baking tin, and used the top of a cooking oil spray can for a cutter. Had lots of sugar solution left over, so I actually made a second batch of cupcakes. I used peppermint oil to flavor the sugar.

    Rave reviews!!!

  11. well i tried to make the chocolate shell but it didn’t work i think that i put to much chocolate because it was really gooey, when i tried to put the cocoa powder on it the powder like socked in and i couldn’t seen to figure out what i did wrong

    • Hi Cole, It sounds like you either used straight chocolate and it came out of temper or something other than the melts, otherwise the chocolate would have just cooled and hardened at room temperature.

  12. well i’m doing this recipe for school and i would like to make it with plain sugar.Is their anything you can tell me that will give me a hint, Ann? Oh and do you think that when doing many geodes at a time with only one saucepan full of sugar solution will make at least 31 geodes or not. Is it hard to make the sugar solution and the chocolate shell, just asking?

    • Hi Cole, start with a small quantity first as it will need practice. Plain sugar isn’t ideal. Better to start with caster sugar or superfine sugar.

  13. Hello there!
    I was wondering about the chocolate alternative to the rock candy geodes you can make. I had trouble with the sugar solution, I followed the steps carefully and it did not turn out the way it showed in the video after 48 hours. Should I have used all the sugar-water solution or should I have measured the huge mixture into two separate bowls and left them that way to cool for the 48 hours? I was just wondering, and I needed some help as I am doing this for a science project for a science fair this Thursday.
    Thank you! 🙂

    • Hi Angel, It sounds like your measurements may have been out. The solution isn’t a large quantity, only 3 cups of sugar and one cup of water. THis makes a super sugar saturated liquid, but only a small quanity. Is that what you used?

      • The temperature is very important, right? I’ve also seen elsewhere that the solution must reach 140C before fast crystallising occurs. I don’t have a sugar thermometer and my geode is still a bowl of sweet liquid after 24hrs. Guess it wasn’t hot enough?

        • Hi Matt, Yes, the temperature is important. The solution needs to get hot enough for the suagr crystals to dissolve, this happens as the solution hits its boiling point. Ann show you this in the video, so as long as the crystals have fully dissolved and the mixture truns clear then you would be at about the right point.

      • well i need help will someone plz

  14. And tried Georgio’s love them making a cake and using them to Adorn it on Sunday thanks for all of your YouTubes now I’m going to try and figure out how to make geode cookies have a great day

  15. Hi! I’m curious as to why the addition of the sugar syrup melts the chocolate egg. Is it because the egg needs a thicker layer of chocolate, or because of the properties of the sugar solution?

    • the properties of the sugar solution i’m guessing because that is what happened to me.

      • Hi Cole, the syrup should never touch the chocolate. You can only add the dried and cooled crystals to the chocolate shell.

    • Hi Julie, There are 2 main things. Firstly the syruo would have residual heat and will melt the cohcolate and secondly because the syrup contains water. Water causes the oil to separate out of the chocolate.

  16. Hi, I was just wondering whether the amount of water would change the way the crystals form or if it will just stay the same.

    • Hi Alisa, If you use too much water the crystals are less likley to form because the mix is less saturated.

  17. Hi Ann I made a rock candy geode myself with a chocolate shell, when I served it I got a lot of questions about how did I make it and how long did it take to make some people were shocked and thought making it was so complicated when I said it took me 3 days to make

    • Hi Kimberly, Your geode looks great and so real. Well done.

    • looks cool and very good.I wish i could make one like that but the sugar solution keeps coming out wrong and very watery.Do you think i put to much water in it?or something else.

  18. I was wondering, Could you use wax paper instead of aluminum or would it stick to the candy? I’d like to make a bunch of small geodes (cupcake toppers) and was trying to think of a way to use a cupcake tin to make lots at once.

    • The advantage of aluminium foil, is the ability to crunch it into a geode shape. You could try baking paper but it wont be easy to shape.

      • wow you are good

  19. Hi Ann
    Ive attempted 3 times to make the geodes shown on your channel . Its just not working for me . The second attempt i thought maybe i wont let the sugar and water boil as much as the first time. But it seems to stay liquid and its not crystalizing . I dont know what im doing wrong

    • Hi Anna, You are more likely to need to let the sugar boil for longer. Make sure the sugar is fully dissolved. Once it is cool it should start to crystallize very quickly if you have used the quantities suggested. Try sprinkling a few grains of crystalised sugar on the surface of the coated geode to kick of the process.

  20. Hi guys! Do you think it will work if I use food coloring that’s like powder? I’m not sure if I’m going to be able to find the liquid one. Thank you for the great idea! 🙂

    • Hi Mari, Gel colors are usually easier to get than the powders, but yes you could use powder in the sugar solution. Make sure it is mixed really well.

      • Hi again! I actually found gel colors as you said and yesterday I tried out the fondant recipe. But it didn’t work. I guess I made the sugar into syrup, but I also noticed that there is lemon juice and vinegar in the food coloring I used. Could that be a problem? And also should I cook the sugar and the water at medium or rather at high heat or it doesn’t mater? Thank you once again! 🙂

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