Mexican Fire Opal
The opal from Mexico plays a small but significant part in the world's opal market. The primary characteristic that sets it apart from the Australian opal is its yellow-orange-red base color. Vibrant flashes of fire emanating out of a rich reddish-orange crystal opal are very striking.
While this is the most prized base color, it is by no means the only base color found in the Mexican material. Mexican opals can have a water base and are seen with a degree of different colors such as yellow, orange, deep red-brown, white, and rarely black. In the event of a black colored Mexican Fire Opal, it is referred to as the “smoked opal.” The treatment for a black colored opal uses hydrophane opals (they lose water content) that are soaked in honey water then heated to deposit carbon in the pores of the opal. The result can be quite attractive or somewhat rough. A smoked Mexican opal has a sticky feel when touched with the tongue or a wet finger because the opal attempts to absorb water.
Another type of Mexican opal is the boulder opal, which is cut using the rhyolite as part of the gemstone. A dark appearance is usually caused by a black coating naturally occurring between the opal and rhyolite, which provides a contrast for the fire in the opal.
When pricing solid Mexican opals, it is necessary to distinguish the three types. There are clear orange and red crystal opals with play of color that are the best that Mexico has to offer. Then there are translucent to opaque orange to white base gemstones with play of color. Finally, there are clear orange base color opals with no play of color. These gemstones are typically faceted rather than cabbed. While the industry calls these opals fire opal, this leads to great confusion as there is no play of color, which is traditionally referred to as fire.
*“About” text is from Opal Identification and Value by Paul B. Downing, Ph.D.
