RARE Carved Fire Agate Cabochon (Mexico) 23x18x10mm. Carved by hand for best fire visibility.  These stones are very hard and the smooth uneven surface makes a really cool ring.  

What Is Fire Agate?

Fire agate is a rare and interesting gem of unusual beauty. It is a brown agate that reflects bright flashes of iridescent yellow, red, orange and green from hemispherical surfaces within the stone. These hemispherical features are a characteristic crystal habit of agate known as a "botryoidal habit".

Fire agate is a phenomenal gem. In gemology, a phenomenal gem is one that reacts with the light that enters it to produce an interesting optical effect. In fire agate, the phenomenon is the iridescent colors. They change as the gem is moved, as the light source is moved, or as the head of the observer is moved. 

 The phenomenon of fire agate is reminiscent of the play-of-color of precious opal, yet it is completely different. The name "fire" is used, but the color is not caused by dispersion - the phenomenon that causes the "fire" seen in diamond.

Fire agate is all about the dynamic iridescent colors.

In fire agate, the botryoidal habit was built as many ultra-thin layers of agate were deposited, one upon another, to produce the unusual shapes that you see in the gem today. Some of these layers of ultra-thin agate were coated with tiny particles of goethite, an iron hydroxide mineral. The colorful "fire" is thought to be produced by interference between light rays as they are reflected and refracted by the ultra-thin layers composed of goethite and agate.