Gemstone Review – Rare Fire Agate
Agate is a form of chalcedony or microcrystalline quartz that forms in layers in a remarkable variety of colors and textures. The most familiar agate is banded agate, which has multicolored layers. Idar-Oberstein in Germany was once famous for its agate mines and agate carving there has a long history, which continues to this day.
Indeed, agate has an even longer history. The ancient Egyptians used agate as a gemstone more than 3,000 years ago. However, one of the rarest forms of agate – fire agate – has been available commercially only in the last 60 years.
Fire agate is a brown agate has a botryoidal (grape-like) form. What is special about fire agate is that it contains platy layers of iron oxide crystals (limonite) on various planes. Iridescent colors of red, gold, green and, occasionally, blue-violet, result from interference between diffracted light rays traveling through and reflecting from these thin layers.
High quality fire agate gemstones can be as impressive in their play of color as fine black opal. But fire agate is much less expensive, even though it is significantly more durable than opal. Since fire agate is a form of quartz with a hardness of 7 on the Mohs scale, it is suitable for any kind of jewelry, including rings.
Fire agate is found in only a few locations in the world, mainly in the Southwestern USA and Mexico. Deposits are found in the area between Kingman, Arizona, Needles, California and around the Colorado River. Fire agate has also been found in some parts of Mexico.
Mexican fire agate specimens come from the mines of Calvillo in the state of Aguascalientes. There are dozens of mines around the mountains of Calvillo. Fire agate is also found in San Luis Potosi and Chihuahua, Mexico. Due to its particular blend of minerals, fire agate from Potosi only has golden fire; rainbow colors are extremely rare.
Cutting fire agate essentially is a reversal of nature’s process, since it requires grinding and polishing away layers, following natural contours, until only the fire is visible. It requires great skill. Removing too much of the chalcedonyreduces the iridescence, whilst removing too little results in a dull appearance. It is painstaking work and since few pieces can be cut in calibrated sizes, fire agate is rarely found in mass-produced jewelry.