Agates are some of the most common stones on the planet. There have been thousands of different agates that have been named and cataloged throughout the world. Some are named for how they form while others are named for their appearances and still others are named for where they are found. Today’s Gem Talk will focus on the geode agate.  A geode is like a tootsie roll pop, underneath the hard exterior is a surprise center!


A geode is a type of agate that starts its formation as a hollow bubble inside of a layer of rock. The outer “crust” of a geode will be older than the crystals that are found inside of it. During the rock formation, the hollow space begins to be filled. This can occur because the outer rock layer is actually porous, although the pores cannot be seen without the aid of a microscope. Which minerals end up inside the geode depends on the location and conditions in which it is formed. For example, quartz crystals are more likely to be found in igneous geodes whereas silica crystals are found in sedimentary-formed geodes.


How do you hunt for geodes? The first step is to start looking in the right location. You can go to visitor’s centers or ranger’s stations as they often have rock hunting guides specific to that area. If you aren’t in a place that has a station, I would consult the Internet to see if there are any places that are known for their geodes. The next step is to know what you are looking for. They are often round or egg-shaped. It is very rare for geodes to be a sharp, pointy rock. They have a tendency to look liked steamed cauliflower on the outside due to the weathering they have endured. They often weigh less than other rocks of comparable sizes due to the hollow centers.

When you do find a geode, you need to figure out a way to break it open. The best method is to use a saw, but since most people don’t have water saws that can cut through rock just lying around in their garage, the next best method is a chisel and hammer. You need to be patient when you chisel it open otherwise you will end up with a shattered mess of crystals and rock. While geodes can be found just about anywhere, a quick Google search suggests that the best place in Illinois is on the western border of Il. And IA in a town called Keokuk, IA. I’m a sucker for family trips that are out of the box, so there just may be a future Gem Talk about our visit to Keokuk, IA.