Fire agates were likely named for their appearance -- their iridescent colors are created by layer structures within the stone, causing a colorful glow -- but their creation really took place in fire. Between 24 and 36 million years ago. volcanic activity caused the silica and iron oxide in hot water to seep into any cracks or spaces it could find. As it hardened, the silica and iron oxide formed alternating layers that create an effect similar to that of mother-of-pearl, but mimics the flickering of a burning ember. Fire agate is found in only a few locations in the world, mainly in the Southwestern USA and Mexico.