Did you know you can Make your own
Geodes? With just a few simple items you can create a crystal of your very own. Fun for you or a
project for the entire family. Anne Marie Helmenstine, Ph.D., a contributor for About.com published and article entitled,
"Crystal Geode Project, Make Your Own Crystal Geode";
Natural geodes are hollow rock formations that contain deposits of crystals. Assuming you don't have a
geological time frame to obtain a geode and don't want to buy a geode kit, it's easy to make your own crystal geode using alum, food coloring, and either plaster of paris or an eggshell.
Crystal Geode Materials
alum (found with spices in the grocery store)
food coloring (optional)
plaster of paris (found in hobby shops) or an eggshell
Prepare the Geode
There are a couple of ways you can go here. You can crack open an egg
and use the rinsed shell as a base for your geode (e.g., as in the copper sulfate geode
project) or you can prepare a plaster of paris
First you need a rounded shape in which you can mold your hollow
rock. The bottom of one of the depressions in a foam egg carton works great. Another option is to set a piece
of plastic wrap inside of a coffee cup or paper cup.
Mix a small amount of water in with some plaster of paris to make a
thick paste. If you happen to have a couple of seed crystals of
alum, you can stir them into the plaster mixture. Seed crystals can be used to provide nucleation sites for the
crystals, which can produce a more natural-looking geode.
Press the plaster of paris against the sides and bottom of the
depression to make a bowl shape. Use plastic wrap if the container is rigid, so that it's easier to remove the
Allow about 30 minutes for the plaster to set up, then remove it
from the mold and set it aside to finish drying. If you used plastic wrap, peel it off after you pull the
plaster geode out of the container.
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Pour about a half cup of hot tap water into a cup.
Stir in alum until it stops dissolving. This occurs when a little
alum powder starts to accumulate at the bottom of the cup.
Add food coloring, if desired. Food coloring does not color the
crystals, but it does color the eggshell or plaster, which causes the crystals to appear colored.
Set your eggshell or plaster geode inside a cup or bowl.
You are aiming for a container that is a size such that the alum solution will just cover the top of the
Pour the alum solution into the geode, allowing it to overflow
into the surrounding container and eventually cover the geode. Avoid pouring in any undissolved
Set the geode in a location where it won't be disturbed. Allow a
few days for the crystals to grow.
When you are pleased with the appearance of your geode,
remove it from the solution and allow it to dry. You can pour the solution down the drain. The alum is
essentially a pickling spice, so while it isn't exactly good for you to eat, it isn't toxic
Keep your geode beautiful by protecting it from high humidity and
dust. You can store it wrapped in a paper towel or tissue paper or inside of a display case.
Follow the above steps and you can have your very own personalized
crystal. Or make as many as you want. Make your own crystals and you may never stop!