What is a Geode Rock Formation
Geodes are a great way to view and learn about the formation of rocks. They occur in sedimentary as well as some volcanic rocks too. These geological rock formations are most commonly limestone on the outside, while the inside is hollow and full of quartz crystals. If there is no air pocket in the formation it is called a nodule instead of a geode.

How Do Geodes Form?

A geode starts off as a bubble or a void left by an animal burrow, tree root, or something else. Water is trapped inside of the void, which contains silica precipitation that has other minerals or elements present in it such as calcite, iron or manganese. The basic crystals of a geode are made of quartz (silicon dioxide) and are colored based on the contents of the surrounding soil.  Over thousands of years different layers of silica precipitation cool and create different layers of crystals. There is no way to tell what is on the inside of a geode without cracking it open. You can view the process of cracking open a geode below.