Offered here is a 4.5" dia. polished agate geode sphere. Blue-gray in color, each layer is visible on the outside while sphere has been polished and includes a 1.25x4" opening to the geode, which allows for viewing the carpet of microcrystals within. Agates are semi-precious gemstones that are a variegated form of chalcedony (a translucent variety of quartz of various colors and waxy luster). Agates naturally develop when an empty pocket inside a host rock is filled molecule-by-molecule, layer-by-layer as microcrystals form concentric bands or other patterns. The colors and arrangement of the microcrystals are influenced by changes in pressure, temperature, and mineral content that occur during the formation process. Unlike other gemstones, each agate is unique. Even slabs cut from the same specimen will vary in color and design. Sphere has a few minor stress hairlines at the edges of the geode opening, but these are only noticeable upon close inspection. This specimen makes for a wonderful display, showcasing the agate geode in both its natural state and in the more commonly seen polished form.