This is quite a coin! These pieces, known as 8 reales provisional money from Real de Catorce, are worth thousands of US dollars if genuine. The coin in our main picture is a fake, worth zero. At the bottom of this page is a genuine specimen from Jesus Vico, S.A. in Madrid. Jesus' coin sold for (are you ready?) 45000 euros, about $59000 US dollars during a 2012 auction.
Rebecca, I hope you have a genuine coin, but the chances are very slim. These coins are extremely rare. (Note: if you think your coin may be genuine, use the Contact Us link to start an e-mail exchange with CoinQuest. If you can send pictures, we may be able to discern real/fake status.)
Here is a summary of Jesus' description of this remarkable coin:
This is a rare piece minted in the first moments of the Mexican insurgency against the establishment in the town of Real de Catorce (present state of San Luis Potosi, Mexico). The name Catorce comes from the adventures of a group of fourteen bandits in the local mountains, where rich silver mines were discovered. After a few years the mining, the settlement was called the Royal Mines of Our Lady of the Immaculate Conception of Guadalupe de los Alamos de Catorce. After that it was renamed Real de la Purisima Concepcion de Catorce and finally, just Real de Catorce.
In September 1810, Mexico enters a complex period face to face with the insurgents. One of them, Jose Mariano Jimenez, from San Luis Potosi, a mining engineer by profession, was put in command of the insurgents and the local population supported him. Informed of the establishment's shortcomings of the lack of cash, Jimenez was given verbal permission to produce provisional coinage and mine authorities agreed to start working pieces of eight (8 reales) containing 30 grams of silver. They circulated for a brief time in the local territory.