The state of Querétaro is the pioneering opal cradle and mining area of central Mexico. In this region the opal deposits are located mainly in the mountain ranges of three municipalities: Colón, Tequisquiapan and Ezequiel Montes. During the 1960s through 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 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. By 1960 there were around 500 known opal mines in this region alone. Other regions of the country that also produce opals (of a 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 be wary of high quality opals from this area. There are also opal mines some small opal mines in Morelos, Durango, Chihuahua, Baja California, Guanajuato, Puebla, Michoacán, and Estado de México.