The UK's Nationwide Geology Club for Children

By Fureya Nelson Riggott FUREYA NELSON RIGGOTT made a fantastic geological recipe book in a previous Rockstar competition. Here we share three of her recipes to illustrate three different kinds of rock: one sedimentary, one igneous and one metamorphic. This is the second, or more specifically, igneous obsidian toffee. Obsidian is a igneous rock type that is a natural glass very rick in silica (around 70%) and low in water. It is formed by the rapid cooling of viscous lava from volcanoes. Obsidian breaks into very sharp pieces, like window glass does. Window glass has a higher silica content. Glass (natural or man-made) doesn’t contain any crystals, so its jagged edges can be just a few molecules thick and be sharper even than a steel razor blade. Also check out Fureya’s other delicious recipes: Sedimentary Oolitic Limestone Crispies Metamorphic Marble Fudge Always make sure you have a responsible adult with you to help you prepare and make your toffee IngredientsMethod You will need: 500 gm granulated sugar 150 ml water ¼ tsp cream of tartar 75 gm butter 100 gm treacle 100 gm golden syrup ** Make sure you are not allergic to any of the ingredients! Oil a 19 cm shallow square tin, or line it with Teflon baking sheet. Measure the sugar and water into a large heavy pan and heat gently until the sugar has dissolved. Add the rest of the ingredients and bring to the boil. Using a clean pastry brush, brush the inside of the pan with cold water, just above the level of the mixture. Bring to the boil. Boil rapidly for 10-15 minutes, or until the temperature reaches the soft crack stage at 143 degrees C. Pour into the tin. Cool for 5 minutes. If you want to mark it into squares, do this now with an oiled knife. Leave it to set in a cool place BUT NOT in the fridge. Or, you can leave it to cool and set, and then do the geologist bit and hit it with a (clean) hammer to break it up, and see the sharp edges. Top tip – this makes a delicious gift for someone you care...