How to make your own geode.
Some of my favorite "rocks" are called geodes. The word "geode" comes from a Latin word meaning "like the earth." This is because when rock hunters find a geode, it looks like an old dirt clod, or maybe a lumpy rock, but almost always it's kind of round. Kind of like the above photo. It's the kind of rock you would like to pick up and throw like a baseball.
There is something special about a geode. A very long time ago, volcanic activity caused the formation of roundish "rocks" that were hollow inside and contained trapped gasses. Over time, ground water seeped into the hollow centers. It replaced the gasses and deposited other minerals, which eventually formed crystals around the hollow walls. This can't be seen from the outside, but when a geode is broken open, you may find quartz in various colors, including rock crystal, purple, pink, and many other colors. Some collectors saw geodes in half to display the beautiful patterns inside. Here are what the insides of two different geodes look like.
Unfortunately, you are not likely to find a geode in your back yard, but you can make your own!
What You Need:
* the top half of a plastic Easter egg
* white craft glue
* a small, disposable paint brush
* food coloring or Easter egg dye
* 1/2 cup of sand
* 1 glass jar, whose mouth is slightly larger than the egg
* a bottle of alum powder. Alum powder, used in making pickles and other foods, is available in many grocery stores. You want alum that contains potassium aluminum sulfate. Two 1.9 oz. bottles of alum by the McCormick spice company is more than enough to make one geode.
What You Do:
1. Coat the inside of the egg-half with a thick coat of white glue. Then sprinkle a generous amount of alum powder to the glue while it is still wet, and let it dry overnight. When dry, pour any extra alum from the egg-half into a cup for use later.
2. Bring 1 cup of water just to the boiling point in a glass saucepan. Let it sit for a minute or two, and then add 20 drops of food coloring and a rounded 1/3 cup of alum powder. Stir until the powder is dissolved. You want what is called a saturated solution, which means all the alum powder that can be dissolved in the water. So add another 1/2 teaspoon of powder, and mix until you can't see it any more. Repeat this until a few alum granules remain in the liquid. Then place the glass saucepan in a microwave for 30 seconds, which should dissolve any remaining granules.
3. Let it sit about 20 minutes, then pour the liquid into the glass jar. Place the egg-half into the jar, open side up, and push it to the bottom of the jar. Let it sit about 15 hours.
4. Remove the egg-half. You should see crystals in it around the inside wall. Place it on a paper towel to dry. (If you make a second one, leave it in the jar for 24 hours, just to see if there is any difference in the crystals.)
5. When the egg-half has dried, turn it upside down on the paper towel and coat the outside with white glue. Pour sand over it so the outside is completely covered. Leave it upside down overnight to dry. If you want a thicker coating of sand, just paint the first coat of sand with glue, and repeat the process.
When it has finally dried, you will have your own geode that looks kind of like an old sandy rock on the outside, but has beautiful crystals on the inside.
What Is the Science? The alum particles in the water and food-dye solution begin to settle out as the solution cools, falling to the bottom of the jar and forming crystals. The alum powder on the inside of the egg-half provides an excellent surface to catch the crystals as they begin to form. You will also see crystals on the bottom and perhaps along the sides of the Glass jar.
If you double the recipe, you can make several geodes. Have fun, and maybe one day you will find a real geode!