Like most agates, crystal stone fire agate is a layered stone, but with microscopically thin layers of silica and iron oxides that allow the light rays entering them to interfere with each other, making colors known as fire. Crystal stone fire agate comes from the class of framework silicates. It is composed from silicon dioxide and has a trigonal crystal system. This rainbow effect, called iridescence, is most familiar in mother of pearl, but it can also be particularly spectacular in crystal stone fire agate. This agate was discovered in the early 1940s.
Because of the limited number of gem-quality localities, crystal stone fire agate is still very rare. Not surprisingly, good specimens command a high price amongst collectors. The habit is curved masses with iridescent surfaces. Because of the layering, which can be uneven, most stones are almost carved rather than cut. Crystal stone fire agate has refractive index between in 1.530-1.539 range and a 0.004 birefringence. En cabochon is the most common cut, used to bring out the iridescence. Crystal stone fire agate has a 0.013 dispersion and none cleavage. Mixed facet cuts have been successful to some extent, and beads and cameos are used, however, the abundance of curvy, asymmetrical shapes makes crystal stone fire agate more suitable for custom crafting. The colors of crystal stone fire agate are available in red, orange, and brown.
Crystal stone fire agate, like all chalcedonies, is believed to be formed when hot water saturated with colloidal silica (a suspension of silica gel) and iron oxide enters cavities in another rock and begins to cool. The luster is vitreous to waxy and crystal stone fire agate has specific gravity in 2.57-2.64 interval. This produces alternating layers of silica and iron oxide (known as schiller layers), and creates the brilliant and unique fire of this gem. In high-quality pieces, this iridescent layering is continuous throughout the stone. The hardness of crystal stone fire agate stopped at 6.5 Mohs level and has conchoidal fracture. More commonly, however, the layering is patchy at best, or, when sustained, weak. The main sources of this exotic natural gemstones are in Mexico and USA (Colorado, Arizona, and California)
