Layer Agate is a semi-precious gemstone which is a diverse form of chalcedony (pronounced kal-sed'-nee), which is silicon dioxide in the microscopic form of fibrous quartz crystal. Natural agate develops when an empty pocket inside the host rock fills molecule-by-molecule, layer by layer as this self-microcrystalline arranges to form concentric bands or other patterns. The color and arrangement of the microcrystals is influenced by changes in pressure, temperature, and mineral content that occur during the formation process. Unlike other gemstones, each agate is unique. Even sheets cut from the same specimen will vary in color and design.