Although nine Mexican states have produced these magnificent gems, Querétaro and Jalisco—two centrally located states—are the primary origins for most opals labeled “Mexican.” And while the “Hecho en Mexico ” label may not be exotic enough for some, these gems are both unique and beautiful.
History. Mexican opal has a long history, dating back as early as the 14th century, when Aztec Indians gathered the gems. Mexican residents still search for opals, digging in open-pit quarries. In this respect, not much has changed since the late 1800s.
But what has changed over the years is the definition of the term “fire opal.” According to some experts, the Mexicans themselves label any opal with play-of-color as “fire opal.” It wasn’t until the 1970s that German gem cutters, looking for faceting material, began attaching the name “fire opal” to transparent non-play-of-color material with yellow-orange to red body color.
Today, to make the moniker more definitive, the term “precious Mexican fire opal” is now used to describe play-of-color cabochon opals with yellow-orange to red body color. Those faceted opals that do not have play-of-color—and which apparently are not precious enough for some—are called simply “Mexican fire opal.”
In the past, the orangey-red to red fire opal—with or without play-of-color—has been called “cherry opal.” Mexican opal also can appear in a variety of body colors, including transparent white, translucent milky white, yellow, green, “gold,” blue, or bluish white (“azul”), and transparent colorless “jelly” or “crystal.”
Color and quality. As with all opal, look for evenness of color as well as evenness of play-of-color. Orange and red body colors are preferred, as are the colors in the play-of-color. There is an extremely 3-D play-of-color that is highly prized. The more saturated the color, the better. Matrix opals are usually of lesser value and therefore kept in matrix, since they can’t be cut into a fine-quality gem.
Prices. The extra-fine-quality material, called Suprema, of which only 3 or 4 stones are found per year, is sold directly to the Asian market. Prices can range from $400 to $4,000/ct. depending on size. Fine-quality Mexican fire opal, called Fina, can range from $200/ct. to $2,000/ct., and even this quality might be difficult to find outside Asia. The Guide lists Mexican fire opal—reddish-orange faceted stones greater than 5 cts., in fine quality and available domestically—at $90/ct. to $175/ct.
Enhancements. There are a few enhancements to watch out for when looking at Mexican fire opal in matrix. Some of the matrix opal with fractures may be opticon-treated. Others may have been assembled to look like true opal in matrix. There is still some sugar- and smoke-treated opal, made to look like Australian black opal, but this material’s appearance practically screams “treated.”
Bench care and cleaning. The water content of opal affects the durability of the material. Sudden temperature or humidity changes can wreak havoc on the gem. So it’s a good rule of thumb to protect opal from any type of repair—and no ultrasonic or steam cleaning! Opal also can be easily scratched or broken.
Use common sense. Stepping out of a warm house into the cold can crack an opal. Placing opals into hot showcases or window boxes can do the same. Humidity becomes a major factor in safe deposit boxes where it’s warm and dry.
For the most part, you can assume that any opal you’re looking at has been out of the ground for some time, long enough for the material to be adapted to your local humidity and temperature. Often, major crazing and fracturing occur in opals in the first few minutes after they’ve been unearthed. Experts know, however, that opals from certain localities can survive nicely for months and then start crazing. Some can become unstable even after a year.
Recommended reading. For more information, see Opals, by Fred Ward, Fred Ward Gem Series, 2000, Gem Book Publishers, Bethesda, Md., as well as Gem Care, also by Fred Ward, Fred Ward Gem Series, 2002, or e-mail: firstname.lastname@example.org.
Special thanks to Steve Jaquith at X.G.X. Corp., New York, specialists in fine Mexican fire opal.