A geode cut in half polished to a high shine showing great banding and crystal formation in the middle.
Measurements: ~ " 1-3/4" tall x 1-5/8" wide x 1/2" deep each half
Location: Beipo Mine, Xuanhua, Hebei Province, China
Geodes are spherical to free form shaped rocks which begin formation as a hollow bubble inside a layer of rock. The bubble could be formed in the lava of a volcano or it could come from the hollow remains of animal burrows or tree roots. As an animal moves out of its burrow or a tree root dies, there remains a cavity surrounded by sediment hundreds of feet thick. The pressure of the sediment eventually causes the sediment around the void to turn into rock. Then, similarly to the geode created by lava, mineral rich water finds its way in and out of the now hardened bubble which allows for the formation of crystal inside the bubble. The crystal formations may be small in form, or may build into larger formations. Normally the mineral deposits are in the form of quartz or calcite. The deposits may be pure thereby creating clear crystallization, or they may have trace elements such as iron, manganese, sulfur, etc. If the formation inside the geode continues to fill it completely it is no longer a geode but becomes a nodule. Geodes are found around the world, with the abundance found wherever there was volcanic activity.