How to create a Geode Cake with a Stone Fondant Effect

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The Geode cake has been such a popular style of cake over the last year or so and this week I’m sharing with you step by step how I made my own version with a stone effect fondant around the outside of the cake.

Ok so firstly before we jump into how I made the cake; what is a geode? In nature a geode is a spherical rock that when broken open has a hollow cavity that is lined with pretty crystals. Think purple amethysts or quartz. So when creating a geode cake we want the cake to look like there are crystals on the inside, and to do this we use sugar crystals.

How to make a geode cake with stone effect fondant tutorial

Click below to watch step by step how to make this cake ⇩

How to make a geode cake with a stone effect fondant – Video Tutorial

Creating stone effect fondant

The geode technique can be added to both fondant and buttercream cakes, but for this tutorial I show you how you can make your cake look like it’s made of stone using fondant. This technique really goes against everything you know about working with fondant, but it is so much fun to do and the finished effect looks so pretty.

For this cake I’ve baked a 5 inch vanilla sponge cake. I actually used the recipe for my 6 inch cake to give me a slightly higher cake. You can find the recipe for my vanilla sponge cake here!

The first thing that I did was marble my fondant with some purple, so it matched the sugar crystals I was going to be using (I’ll be getting to those soon). Now for the next step you want to have thought ahead. The night before I left out some fondant, uncovered on my surface to dry out. You’ll see in the video I could still squish it a little but when I crumbed it down I got dried lumps of fondant. You want to mix these into your dried fondant. I know you probably think I’m mad at this point!

How to make your fondant look like stone

I then started to roll out the marbled fondant, but when it was around 2cm thick I tore off large pieces and patchworked them back together. This can give you little tears in the fondant, but that’s ok, that’s what makes it look like stone. You then want to smooth it down onto your cake and fill in any gaps. The fondant has a real rustic appearance, and on any other cake you might worry your finish isn’t great, but combined with the geode effect it is the perfect finish.

Create the Geode Effect

Once the cake was covered I used some of the cracks in the fondant to work out where I wanted the crystals to go, using the cracks as part of the design. I always find marking out where I’m going to cut first with a dresden tool is really helpful as you can alter it before cutting.

Cutting the hole for a geode cake

I cut 2 areas, one at the top and one at the bottom. At the bottom you want to make sure you don’t cut too deep as you don’t want to make the cake unstable. Also remember the larger the holes the more sugar crystals you’re going to need to add and this can take ages.

geode cake sugar crystals

You then want to add your sugar crystals. I found tweezers the easiest thing to use, but you will be adding them one by one. For the crystals I used the pre-coloured sugar crystals by Halo Sprinkles and you can find a 10% off discount code below. You can use white ones and mix a little gel colour with rejuvenator spirit or dipping solution and paint them once they’ve been added, but using the pre coloured ones was so easy and the colours to choose from are amazing.

gold edible paint on a geode cake

I loved the cake before, but finishing off around the edge of the crystals with a gold edible paint, was the perfect finishing touch. I used some of the glamorous gold lustre dust by Sweet Sticks and mixed this with a little dipping solution, just dabbing my brush against the edge of the outer crystals.

The Sugar Crystals – Plus 10% off

As I mentioned above I used the pre coloured sugar crystals by Halo Sprinkles. In my opinion these are a game changer when it comes to the geode cake as they speed up the process so much with you no longer having to paint the crystals yourself (unless you want to), and they come in so many pretty colours.

Halo sprinkles sugar crystals

For this cake I used the purple, lavender, pink and white crystals.

Sugar crystals for a geode cake

Halo Sprinkles have kindly given me a 10% off voucher code for you to use. This can be used on any purchases made on their website. To receive the 10% off all you need to do is visit their website and enter HaloLynz10 at the checkout.

Plus you can also get the sugar crystals on the Sweet Stamp website too. Just visit and enter the code CAKESBYLYNZ at the checkout!

The finished Geode cake

I really loved creating this cake and I really hope you enjoyed this tutorial and will be able to use some of these techniques on your own cakes, whether you are creating a one tier birthday cake, or maybe a multiple tiered wedding cake.

Geode cake with a stone effect tutorial

If you haven’t already you can subscribe to my YouTube channel for more Free cake decorating video tutorials.

Tools I used

I have put a list below showing all the tools that I used throughout this video or if you would like to see all my favourite cake decorating tools just click here:

Halo Sprinkles Sugar Crystals: (Use code CakesbyLynz for 10% off)
Halo Sprinkles Sugar Crystals at SweetStamp – White: (Use code CakesbyLynz for 10% off)
Halo Sprinkles Sugar Crystals at SweetStamp – Purple: (Use code CakesbyLynz for 10% off)
Halo Sprinkles Sugar Crystals at SweetStamp – Lavender: (Use code CakesbyLynz for 10% off)
Halo Sprinkles Sugar Crystals at SweetStamp – Pink: (Use code CakesbyLynz for 10% off)
SweetStamp Brushes: (Use code CakesbyLynz for 10% off)
SweetStamp Edible Glue: (Use code CakesbyLynz for 10% off)
Dipping Solution:
Turntable: UK – USA –
PME Cake Smoother 10inch:
Colour Splash Violet Get Colour:
Plastic Smoothers:
Squires Kitchen Belissimo Flexi Smoothers:
King Pin Rolling Pin:
Glamourous Gold Lustre Dust:

~ Please note that some of links above may be affiliate links. If you click the link and purchase any item through that link, I will receive a small commission from the website but this does NOT add any additional costs to you. Thank you so much for supporting this blog x ~

Plus why not save this tutorial for later and pin it to Pinterest

stone effect fondant geode cake tutorial

Thank you for reading!

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Hi, I’m Lynsey and welcome to Cakes by Lynz. I LOVE everything cake! Here you will find all my latest cake decorating video tutorials from my YouTube channel, reviews and general cake ramblings!

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