Quartz pendant Mexican Fire Agate Pendant (2021) Design par Alberto Thirion

Mexican Fire Agate Pendant

The total weight of the pendant, 7.8 grams

The measure from tip to tip, 38x22.5x7 mm

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” created by the layers of nacre on the surface of pearl.) Looking at a fire agate is much like looking down into the burning embers of a fire, which is exactly how it got its name. The gem is thought to be formed when hot water saturated with colloidal silica and iron oxide invades cavities in country rock and begin to cool. Chalcedony with iron oxide begins to grow on any available surface (the iron oxide gives the basic brown color to the gem). As the solutions began to precipitate and grow layers of silica and iron oxide would be deposited depending on the relative level of those elements in solution and underlying conditions. These alternating silica and iron oxide layers (Schiller layers)) cause the brilliant fire in the gem. As iron oxide ran out in the solution colorless chalcedony continued to grow.

Definition-Schiller layers: One of a series of layers formed by sedimenting particles that exhibit bright colors in reflected light, because the layers are separated by approximately equal distances, with the distances being of the same order of magnitude as the wavelength of visible light. Also known as iridescent layer.

Fire agate is found only in the US Southwest —the land between Kingman, Arizona and Needles, California and around the Colorado River— and Mexico. It wasn’t sold commercially until after World War II.

Fire Agate is one of the most difficult opaque materials to cut properly. In order to best reveal the colors, the overlying layers of chalcedony must be very carefully removed from the botryoidal surface creating a freeform shape with a carved upper surface. Just a bit too much material removed kills the iridescence and too much left on dulls it. Such painstaking treatment requires substantially more time per piece by the lapidary, and tends to elevate cost. This type of fashioning also leads to a lack of calibrated pieces and has prevented the use of this gem in mass produced jewelry items. This, combined with the fact that it is found in so few locations, keeps it scarce and mostly unknown to the general public.

It is very long wearing and tough material which may be worn every day.

Thèmes connexes

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