What is Fire Agate?

Fire agate is a brown, microcrystalline quartz (chalcedony) which has a botryoidal (grape-like) growth form, and which contains layers of plate-like crystals of iron oxide (limonite) in various planes within it. The layers are small enough that light entering them forms interference colors known as "fire." The iridescent colors of red, gold, green and rarely, blue-violet, result from interference between diffracted light rays traveling through and reflecting off of these thin layers. (We see the same effect when looking at the rainbow colors at the surface of an oily puddle of water; or in the "orient"