What is a Geode?
A geode is an unusual, rounded mineral formation typically with an exterior shell of chalcedony (very fine-grained quartz), with other minerals and / or crystals lining the interior. The name geode is from the Greek geo referring to the shape of the earth, since most geodes are spherical. A geode can form in any cavity within a rock, but the most common method for geode formation is via gas bubbles that form in cooling ash beds. The bubble gets “frozen” in place when the silica rich ash / dust hardens. The partial or complete filling of the bubble may occur immediately or even thousands to millions of years later and can encompass a variety of different minerals. Geodes can also be filled with surrounding silt and sediments, forming a “mud ball.” If a crystal breaks off inside the geode, you can hear rattling (the only guarantee of a hollow geode!), hence the nickname “rattlestone”. Occasionally, water gets trapped in the geodes, forming what is called an enhydro, Greek for “water insi
A geode is a rock, with a rough and insignificant looking exterior, that is either partially or completely filled with crystal. The geo prefix means earth, and the rough lumps on the outer surface are often spherical, resembling small planetoids. Petrologists do not really have a clear understanding of how a geode forms. It is theorized that round geodes formed from bubbles in volcanic rock, while the crystals formed later, with the slow seeping of mineral-laden water into the bubble. Irregularly shaped geodes are perhaps formed in cavities created by ancient roots or burrows. Any number of precipitating crystals can form inside a geode. Smooth crystal such as agate can entirely fill the cavity, and split agate geodes of various colors make attractive bookends for rockhounds. Perhaps the most beautiful geode is a an amethyst geode, filled with deep purple amethyst crystals all pointing inward. Amethyst geodes are mined in Brazil and Uruguay, with Uruguay producing geodes of the deepest
The mysterious earth-shaped geodes have long challenged geologist to explain how they are formed. Geodes are a variable phenomenon and, therefore, many theories exists to explain how they are created. The term geode is derived from the Greek word Geoides which means “earthlike.” A geode is a sphere shaped rock which contains a hollow cavity lined with crystals. A geode which is completely filled with small compact crystal formations such as agate, jasper or chalcedony is called a nodule. The only difference between a geode and a nodule is that a geode has a hollow cavity, and a nodule is solid. How Geodes Are Created Geodes begin as bubbles in volcanic rock or as animal burrows, tree roots or mud balls in sedimentary rock. Over time, the outer shell of the spherical shape hardens, and water containing silica precipitation forms on the inside walls of the hollow cavity within the geode. The silica precipitation can contain any variety of dissolved minerals, the most common being quartz,
The mysterious earth-shaped geodes have long challenged geologist to explain how they are formed. Geodes are a variable phenomenon and, therefore, many theories exists to explain how they are created. The term geode is derived from the Greek word Geoides which means “earthlike.” A geode is a sphere shaped rock which contains a hollow cavity lined with crystals. A geode which is completely filled with small compact crystal formations such as agate, jasper or chalcedony is called a nodule. The only difference between a geode and a nodule is that a geode has a hollow cavity, and a nodule is solid.
