Fire agate is associated with the chalcedony group of microcrystalline quartzes. They are either solid-coloured stones, or have bands or moss-like or dendritic inclusions (agates). The distinctive iridescent colours of fire agate come from layers of iron oxide inside the quartz. This rainbow effect might be presented by cutting in cabochon.
Fire agate can be found in Arizona (USA) and Mexico.
Iris quartz includes a similar iridescence, but this really is brought on by internal cracks.
