How does a geode form?
K.S. Peabody A. A geode is a hollow, globe-shaped rock that can contain beautiful mineral crystals. Geodes are usually just a few inches wide, although sometimes larger ones are formed. Although a geode can have a spectacular crystalline interior, they can appear quite ordinary from the outside. Geodes are made out of limestone. According to Richard Murray, an assistant professor of earth sciences at Boston University, because limestone rocks dissolve relatively easily, cavities can form inside them. These cavities give the crystals a chance to form. The crystalline structures inside the geode are made up of minerals that came from outside the rock. Minerals dissolved in water that circulates around a limestone rock are able to percolate into the inside of the rock through tiny holes in the limestone. Once inside the limestone rock, the minerals can form the crystals — including layers of different colors. “The layers are caused by different generations of fluids,” says Murray. The
