A geode looks like an ordinary igneous or sedimentary rock, but the inside is often full of crystals! You can find geodes "in the wild" in some parts of the country, or at rock shops or science supply stores.
Watch our project video to see us crack open some geodes and find crystals inside:
What You Need:
Buy the supplies for this project in one convenient kit!
Geodes are formed when there is a hollow cavity in solid rock. This cavity can form in several ways: by a gas bubble in a lava flow, by limestone being dissolved by an acidic substance, or by a shell not being filled completely with sediment when it is fossilized. When mineral-rich ground water gets into these cavities, the minerals can form crystals, depending on the temperature, pressure, and the amount of water. (Go here to learn more about crystals.)
Each geode is unique. Some will have large colorful crystal formations, others may have solid bands of quartz, and still others will have mineral deposits but no crystals formed yet. Sometimes a geode might be full of silt or sediment. This kind is called a "mud ball." If you are selecting your own geodes, try to choose ones that seem light for their size; these are more likely to be hollow in the center and have crystal formations.
For a fun activity you can do with household materials, check out our Make Your Own Geode project!