Editing Opal (section)

=== Mexico ===

Fire opal is a transparent to translucent opal with warm body colors of yellow to orange to red. Although fire opals don't usually show any play of color, they occasionally exhibit bright green flashes. The most famous source of fire opals is the state of [[Querétaro]] in Mexico; these opals are commonly called Mexican fire opals.<ref>{{cite journal |last1=Koivula |first1=John |title=Opal from Querétaro, Mexico: Occurrence and Inclusions |journal=Gems & Gemology |date=1983 |volume=19 |issue=2 |pages=87–96|doi=10.5741/GEMS.19.2.87 |doi-access=free }}</ref> Fire opals that do not show a play of color are sometimes referred to as jelly opals. Mexican opals are sometimes cut in their rhyolitic host material if it is hard enough to allow cutting and polishing. This type of Mexican opal is referred to as a Cantera opal. Another type of opal from Mexico, referred to as Mexican water opal, is a colorless opal that exhibits either a bluish or golden internal sheen.<ref name="LetsTalk">{{cite web|first1=James|last1=Swisher|first2=Edna B.|last2=Anthony|url=http://www.attawaygems.com/NMFG/Lets_talk_gemstones_opal.htm|title=Let's Talk Gemstones: Opal|url-status=live|archive-url=https://web.archive.org/web/20111107214533/http://www.attawaygems.com/NMFG/Lets_talk_gemstones_opal.htm|archive-date=7 November 2011|df=dmy-all}}</ref>[[File:Precious Mexican Fire Opal with attached matrix.jpg|thumb |left|alt=A specimen of recently mined Precious Mexican Fire Opal. The background host rock (matrix) has characteristic pink-white coloration.|Precious Mexican Fire Opal has bright green and yellow patches (play of color) with an orange-red background typical of Fire Opal.]]
Opal occurs in significant quantity and variety in central Mexico, where [[mining]] and production first originated in the state of [[Querétaro]]. In this region the opal deposits are located mainly in the mountain ranges of three municipalities: [[Colón, Querétaro|Colón]], [[Tequisquiapan]], and [[Ezequiel Montes]]. During the 1960s through to the mid-1970s, the Querétaro mines were heavily mined. Today's opal miners report that it was much easier to find quality opals with a lot of fire and play of color back then, whereas today the gem-quality opals are very hard to come by and command hundreds of US dollars or more. The orange-red background color is characteristic of all "fire opals," including "Mexican fire opal".

The oldest mine in Querétaro is Santa Maria del Iris. This mine was opened around 1870 and has been reopened at least 28 times since. At the moment there are about 100 mines in the regions around Querétaro, but most of them are now closed. The best quality of opals came from the mine Santa Maria del Iris, followed by La Hacienda la Esperanza, Fuentezuelas, La Carbonera, and La Trinidad. Important deposits in the state of [[Jalisco]] were not discovered until the late 1950s.

In 1957, Alfonso Ramirez (of Querétaro) accidentally discovered the first opal mine in Jalisco: La Unica, located on the outer area of the volcano of Tequila, near the Huitzicilapan farm in [[Magdalena, Jalisco|Magdalena]]. By 1960 there were around 500 known opal mines in this region alone. Other regions of the country that also produce opals (of lesser quality) are [[Guerrero]], which produces an opaque opal similar to the opals from Australia (some of these opals are carefully treated with heat to improve their colors so high-quality opals from this area may be suspect). There are also some small opal mines in [[Morelos]], [[Durango]], [[Chihuahua (state)|Chihuahua]], [[Baja California]], [[Guanajuato]], [[Puebla]], [[Michoacán]], and [[Estado de México]].