About- OPAL from Queretaro:
Queretaro is the center of opal mining and cutting in Mexico. Mexican opal has been known since the latter part of the 18th century, but the more familiar gem quality material has been available to the world market only since the end of the last century. At times, the beauty of Mexican opal exceeds that found in opal from any of the world’s better-known deposits, such as Australia. The most important opal deposits in Mexico are in the state of Queretaro, although there are other significant deposits in the states of Chihuahua. Queretaro opal is often distinguished from another opal by its unusually high degree of transparency and by its particularly vivid red and green play of color. Although the cabochon is the most common cutting style, the transparency of the Queretaro material occasionally allows it to be faceted, a cutting style not generally considered for opal. A reddish orange body color is most commonly seen in fine opals from this area (responsible for the term fire opal), with a predominantly green play of color that may be in broad spangles, small flecks, or even pinfire.
(reference) Opal from Queretaro – GEMS & GEMOLOGY Summer 1983
Probably the most damaging misbelief about Mexican opal is that it dehydrates and cracks far faster than another opal from other localities. Opal is a delicate stone and opals from any locality may crack with age. The highest quality opal from anywhere, however, if cared for properly, is a potential heirloom. Antique opal jewelry is seen in many museums and private collections, and this is true of fine Mexican opal as well as opal from Czechoslovakia or Australia. Opals from Aztec ruins hundreds of years old have been found with no cracks in them at all.
(reference) Queretaro Opals - Lapidary Journal June 1987