Have you ever seen a geode? On the outside, it looks like a plain old, round rock. But when you break it open, inside is a lining of beautiful crystals!
Geodes are found all over the world, usually in deserts. If you live in any of the southwest or midwestern states, you might be able to find them out in nature!
You can also find them for sale at toy and rock shops to take home and break open yourself.Geodes start out as tree roots, mud balls, or volcanic bubbles inside of sedimentary rock. Over many millions of years, the outer, rounded shell hardens, but the inside remains hollow.
A liquid containing dissolved minerals gathers on the inner walls of the geode. Over time, these minerals form crystals!
In this experiment, you can create some geode-like crystals using eggshells and a few items from home. The science is similar to how a real geode is made, but on a shorter time scale - 20 minutes instead of millions of years!
NOTE: Setting up the lab will only take about 20 minutes, but once you're done you'll have to wait overnight to see the full results.
What You'll Need
WHAT'S GOING ON?
You probably noticed that the borax powder dissolved easily in the hot water. More borax will dissolve in hot water than in cold water. Hot water molecules move around a lot more and there is more space between the molecules. So there is more space to hold the borax. This type of solution is called a supersaturated solution. The water can not hold any more borax - it's completely stuffed!
When the solution cooled overnight, the water molecules slowed down and got closer together. There was no more room for the borax, so it could no longer remain dissolved. The borax particles came out of solution and settled on the eggshells, in the form of crystals!
What is a Crystal?
When molecules like borax (a mineral salt) come together in a very organized, patterned way, a crystal is formed. The size and shape of the crystals depends on how fast the solution cools. When solutions cool fast, smaller crystals are formed because they have less time to organize. Slow-cooling solutions tend to form larger crystals. You might want to repeat the experiment again, but this time, try putting the glasses into the refrigerator overnight. What do you think will happen to the size of the crystals?
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