Geode Set

Geodes form in cavities in rock close to the surface over thousands or even millions of years. They don't need pressure or heat to form. As the surrounding soil weathers away, the hard geode nodules are left behind for us to find! Rock cavities can originate from bubbles in lava that cooled quickly, or from gaps in sedimentary rock. These gaps could be from something organic (previously alive) decomposing, and can even form in dinosaur bones! Water squeezes through tiny holes into the cavities. The water carries silica and other dissolved molecules in it. These can start to adhere to the sides of the cavity and begin making bands of agate (chalcedony - microcrystalline quartz). These can crystallize pretty quickly, but the longer it takes to crystallize, the bigger the crystals can be and that's why you get quartz crystals. Quartz crystals with a little bit of iron become purple amethyst. This set of two geode halves contains one agate half-geode with beautiful colorful banding (from R