Before we go through the process of how geodes are made, it is important to understand first what it is. Geode is a rock formation combining minerals to produce hollowed-out rock that have crystal linings on the inside. It could take a long time to form the geodes.
Some geodes that were found are actually thousands to millions years old and when they are split in half, you can see different layers that include the hollowed out center, mineral deposits and crystal deposits.
Geodes are formed or produced by starting out a hollow bubble within the rock layer. These are formed from volcanic rock which gives the best idea of how it is made. Volcanic rock is formed from cooled molten lava. When there are air bubbles appearing, it presents the opportunity for geode to form. This takes place while the air bubble is warm.
When rain pours down to the rock layer, the chemicals from the rock are then released into the water. The water will be absorbed and undergo the hard rocky outside layer and it gets trapped into the inside of the bubble. This could last for few seconds in order for the mineral rich water to have those small particles cling into the inside of the air bubble. These particles will turn into crystals from water moving constantly through the bubble and then the water depositing more minerals inside of the air bubble.
The crystals that vary in sizes and shapes appear depending on how the geode has long been forming and on how water was moving into the air bubble. The geodes are produced into the hollowed out animal borrows and tree roots.
When the geodes are formed and cracked open, different colors, sizes and shapes of crystals will show. Not all geodes are the same since the rocks that contribute to their formation differs in types. The chemicals that were being released by the rocks to the water pass through the air bubbles are filled with minerals. The different minerals clinging into the interior of the air bubble will cause the varying colors of crystal that forms the geode.