Geodes and Geode Slices

A wondrous and unique occurence of Mother Nature, geodes form in a wide variety of shapes, sizes, and colors. They can be found in the southwestern U.S., Mexico, and Uruguay (to name a few), although Brazil is the primary source. They are formed by a high content of silica solutions seeping into a hollow which is often spherical in shape. With the help of volcanic activity heating the ground, thin bandings of agate form on the outer layers, working their way inward. A crystallization of the mineral quartz takes place, and the slower the cooling, the larger the crystal inside. Occasionaly secondary minerals such as calcite, hematite, and rutile also form from other solutions entering later.