Fun with crystals

Fun with crystals

If you look closely at sugar or salt, you will see it is made up of lots of little crystals. We can ‘grow’ bigger crystals if we start from scratch and let them form slowly. So how do we make a crystal from scratch? We need to dissolve the salt or sugar and then let it recrystalise. You can try out these two experiments to make some rock candy and geodes. Both of these involve boiling water so definitely one for some grown-up help.

Rock candy

Heat a cupful of water in a pan until it is boiling. Then start adding sugar. Stir, add more sugar, stir, add more sugar, stir…you get the idea! Keep going until you cannot get any more to dissolve, this should be at least two cupfuls. This is called a saturated solution. Let the mixture cool down for around 20 minutes then pour into a tall glass. When the solution cools we say it supersaturated, this means it now has more sugar than it can normally hold. It’s ready to start growing crystals! If you hang a bamboo skewer into the glass (use a clothes-peg to keep it in place), crystals of sugar will start to form on the skewer. Remember we need SLOW formation so it will take a few days, perhaps even a week, be patient! It’s really important that it is left undisturbed for this time so put it somewhere out of the way.

Geodes

Geodes are mineral crystals found inside rocks, we can make our own inside eggshells. Make sure the eggshells are perfectly clean and the membrane has come away from the inside. Make a saturated solution like you did before, you can use sugar or try table salt or Epsom salts, then add a little food colouring. Pop the shells in an egg box and fill with this solution, the fuller the better but make sure they won’t spill! Leave them somewhere safe to evaporate and in a few days you should see the geodes form!

Crystals in nature

Crystals form in nature when some things become solids. This can be rocks that were molten (lava) or minerals that were dissolved in water. Molten rocks will solidify as they cool, dissolved mineral will crystalise as the water evaporates.

The size of the crystals depends on the time that they take to form. Fast=small, slow=big. Igneous rocks (ones that are made from lava or magma) might have small crystals if they came from a volcano as they would cool quickly in the air. Sometimes igneous rocks can be made slowly underground and we can often see larger crystals in these. Geodes come from dissolved minerals seeping into gaps in other rocks, the water evaporates soooo slowly that we get beautiful big crystals. You can try putting your egg geodes in different places when they are evaporating, perhaps one on a radiator, one on a windowsill and one somewhere cold. Just make sure they’re not going to get knocked over!