Superb Contra Luz Fire Opal. A Published Gemstone, Magdelena, Jalisco, Mexico. Estimate US$ 40,000 - 50,000 '€37,000 - 46,000). Photo Bonhams.

Perhaps the finest contra luz opal to appear at public auction, the present example has been contour polished to follow the lines of the original rough to fully reveal its inner beauty. A deep, rich mandarin orange in body color, the spectral colors appear in bands of green, yellow, orange and crimson red--completely reminiscent of an aurora borealis phenomenon. This is an exceptional opal for the knowledgeable collector. 

Opals were formed during the Cretaceous period and brought to the Earth's surface during the Pleistocene age. There are 25 or so varieties of opals but the most significant fire opal deposits are found in Mexico. One of the two largest sites for mining Mexican fire opal is located near Magdalena, Jalisco, a small city located approximately 100 miles east of Vallarta. Magdalena is in a region laden with igneous rocks, obsidian, volcanic lava, and more than 300 opal mines. 

Mexican fire opals consist of silicon dioxide or silica spheres arranged in an orderly pattern with iron oxide dispersed throughout giving the fire opal its distinctive brilliant flame-like colors of yellow, orange, and red. The three most important attributes of the fire opal are body colors, transparency, and play-of-color (differing colors when viewed from various angles). Simply put, the greater the play-of-color, the more precious the gemstone. Because most opals are not faceted, they are generally displayed in the cabochon form; however, fire opals are often the exception.

Mexican fire opal was known by the Aztecs and was used by Mayans as well for ritualistic purposes and in various mosaics. Even today many connoisseurs believe that fire opals bestow courage, stamina, and energy to the wearer due to its warm, fiery orange-red colors. 
Weighing approximately 29.65 carats and measuring 29.78 x 20.95 x 12.42 mm 

Accompanied by a copy of the book distributed at the Thirteenth Annual Sinkankas Symposium: Opal, held April 18, 2015 at GIA World Headquarters, Carlsbad, California in which this opal is illustrated on page 119. 

Bonhams. THE WORLD OF OPALS, 23 Nov 2015 15:00 PST - LOS ANGELES