How can you tell if a rock is a geode?

To crack open a rock to see if it's a geode, I recommend getting a good quality rock hammer. Your typical carpenter's hammer is not the ideal tool for the job, so get a good rock hammer (an estwing hammer is probably the most common one that I see geologists work with). These hammers are different from regular hammers because they are reinforced steel, where the steel is made stronger by adding other metals into it. Make sure you wear safety goggles and gloves, too.

There are some physical clues that a rock is a geode that you can look for when you're rock hunting. Geodes are usually round or egg-shaped, and they tend to have a bumpy exterior. They also feel lighter than other rocks since they have a hollow space inside. You can't be sure without breaking the rock open, but these are some signs you can look for!