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 rich 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:
Featured as part of the Virtual Festival of Geology 2020
Igneous Obsidian Rock
Igneous Obsidian Toffee
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.
