Fire Agate is a unique and beautiful stone, a variety of chalcedony that has an opalescent play of colors. Kind of like a fire opal. It is only found in parts of the southwest United States, California, and Mexico. It is thought that the stone, which has a large iron oxide component, builds up in layers, from solution. Silica, the component which gives opal its wonderful play of color, is a factor in the formation of Fire Agate. The iron oxides normally give the stone a dark brownish body color, although some mines produce material with more of a golden tone.
Over the last several years, a material has been marketed in the gemstone trade under the name “crab fire agate”. This material is not Fire Agate whatsoever. Crab Fire Agate is treated carnelian, sardonyx, or agate. When it is heat treated it creates a spider web pattern in the stone. However be careful, some of the material being sold as “crab fire agate” appears to be a man-made material, possibly a glass or ceramic material.
Both Fire Agate and Crab Fire Agate are genuine stones with their own unique properties and looks.