How to Make A Purple Geode Cake

I finally hopped on the geode cake band-wagon this weekend, and found that it is WAY easier to make a geode cake than I thought!

All you need is a frosted cake, some white/clear rock candy, gel food coloring, and a little vodka!

I was inspired by an amazing amethyst/geode wedding cake made by Intricate Icings Cake Design. To help the purple pop even more, I added a gold border with edible gold paint.

I modified the design to make it a bit more approachable for all of us home bakers!

The Cake Components

This cake is made with my favorite vanilla layer cake recipe, which I colored purple with gel food coloring.

I baked four, eight-inch round cake layers using 1 batch of cake batter. The cake is frosted the cake layers with 1 batch of my American buttercream.

Creating the Geode

Once the cake layers were stacked, I covered the cake in a thin crumb coat. Then I trimmed a triangle from one side of the cake.

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Next, I covered the exposed area with frosting, and let the cake chill in the freezer for about 5 minutes, until the crumb coat is firm to the touch.

Add a second layer of frosting, and smooth using a bench scraper.

Gently press crushed rock candy into the cut area of the cake.

I started with the larger chunks of candy, then filled in with smaller bits of candy.


Coloring the Geode

Mix together a few drops of vodka and large squeeze of purple gel food coloring.

Using a kitchen paint brush, gently dab the mixture into the center of the candy area.


Rinse off and dry your paint brush, and add some additional vodka into the gel food coloring to dilute the mixture.

Brush around the dark purple center, gradually spreading the lighter purple liquid out towards the edge of the candy covered area.

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Leave the rock candy around the edge uncolored. The final step is to paint the edge of the candy area with a boarder of edible gold paint.Β 

You could also use edible gold leaf on the border.

And that’s it! It’s that easy!!! If would also be fun to use a grey buttercream (or even an oreo buttercream), to make the cake look more like a rock.

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56 thoughts on “How to Make A Purple Geode Cake

  1. My daughter desperately wants to make this for her birthday? Where do you find such big chunks of rock candy? I’ve only seen it on a stick or on a string.

    1. they’re that kind! I’ve simple broken them off the string or stick, and placed the small chunks into the frosting! it takes a big of time, but it’s worth it πŸ™‚

  2. Thank you for the tutorial! I’m making my own rock candy, so I will just color it at that time. You made this look very approachable!

  3. Hi Chelsweets! Can I put the whole cake in the refrigerator once it’s finished, or will the buttercream get weird?

    1. You definitely can, I do that all the time! just be sure to let it slowly warm to room temp the next day, to minimize the risk of condensation! The buttercream will crust as it’s exposed to the air, but it doesn’t change the taste at all!

  4. I know this question has been asked but where did you purchase the strings of rock candy for this cake? I am getting married with a geode cake but the baker can’t find the right rock candy to use..

    1. i probably used about 12 rock candy sticks! but it can vary depending on how large of a cut you make, and how big your cake is!

  5. Hi Chelsea. Will this work on a textured cake
    like Italian cream or carrot cake with cream cheese frosting instead of butter cream? Any advice is greatly appreciated ?

  6. Thanks for sharing this! I want to make one for my daughter’s 30th! How thick are each of the layers? You said they are 8″ but they look much flatter. Thanks!

  7. Hi, a question on cake and buttercream recipe.

    β€œI used my favorite vanilla layer cake recipe (bakes perfectly flat), which I colored purple with gel food coloring.

    I baked 4, 8-inch round cake layers, and frosted the layers with american buttercream (I used 1.5 batches).”

    Did you take 7inch cake recipe and took 1.5 times? Also 1.5 times recipe from you 7” buttercream recipe?

    1. I make one batch of cake layers to make four, eight inch layers! My layer cake recipe can be used to make seven or eight inch cake layers, it just makes less thick layers when they’re 8 inches across! I didn’t want this cake to be too tall, so I made the layers 8 inches.

      The second line you included means I made 1.5 batches of buttercream frosting! I updated the wording to make it more clear that I’m referring to the frosting. Hope that helps, I’m so sorry for any confusion ??

      1. I’d say it was about 6-7 inches tall! but it can vary based on much frosting you add between your layers <3

  8. I followed your advice on the coloring geode white candy using vodka and americolor last nighy but the rocks are still wet and leaving color all over my fongers . What do i do to fix this

    1. it sounds like you may have used too much gel food coloring! You should only add a couple drops to about 1 teaspoon of vodka, and it should dry within an hour! you can try to point a fan at the cake on a low sped to accelerate the drying <3

  9. Love this cake! Thank you for sharing how you accomplished it. Can I gel color (and let them dry) the rock candy before I pat them into the cake? I think that would be easier for me.

    1. I’ve never tried it that way before, but as long as they’re fully dried, I think that should work! I’d love to hear if it works, let me know how it goes, Vicki!

    1. I think I used about 2 lbs of rock candy, and I had a little left over!! I had to break it off the sticks, so a lot of it got crushed into tiny pieces I couldn’t use :/

  10. Love this cake, I am going to try this today. My only concern would be putting it in the fridge. I know what will happen to the buttercream with the condensation but was wondering how the rocks react to being in the fridge over night, and taken out for an event the next day?

    1. The rocks should be fine as long as the cake is kept indoors / in an air conditioned room once it’s out of the fridge. I live in NYC, and the only time I have issues with condensation is when I take cakes straight out of the freezer. If you live in a really warm or humid environment though, you may have more condensation that I’m used to <3

  11. im making a 4 tier geode fake wedding cake, in the middle will be an open heart, im covering it in fondant and inside the heart will be the rock candy my concern is i was going to use piping gel to stick the rock candy to but i dont think it will be strong enough to hold the candy upside down in the heart, do you think i should use royal icing or any other ideas?

    1. Hi Gina,

      I would be worried about that too, I don’t think piping gel would be strong enough! I’d say try royal icing, or even secure it into the cake using a wire or skewer!! Anything that defies gravity makes me nervous!! I hope that helps, please let me know how it turns out <3

    1. I’m so sorry! Sometimes it takes me a while to approve and respond to comments, but I usually get to it once a week! Hopefully you see your comment and my response to it now <3

  12. Hi! I was wondering how this would keep? I want to make the cake completely one day and serve it the next. Will the candy rocks go bad? Thanks!

    1. Hi Michelle! It should keep fine overnight in the fridge. If you live in a really warm or humid place you might have some condensation, but this time of year you should be ok! Hope that helps, happy baking!

      1. Thanks! I did end up putting it in the fridge and it turned out wonderful. The rock candy remained crunchy too. My family loved it. Thanks for the recipe!

    1. hi Lauren,

      for sure! You can use a clear extract like lemon or almond to dilute the food coloring. Hop that helps, happy baking!

  13. Hi Chelsy, could I make this as a 6” cake or do you think the geode design would have to be too small to be proportional to the cake?

Let me know what you think!