Opal was known to the Aztecs by the name Vitzitziltecpa which means humming birdstone, due to its similarity to the bright iridescent colours of the birds plumage. The original mining locations were lost during the Spanish conquest. They were rediscovered sometime in the early 1800's,by Sir Maria Siurab, in the state of Queretaro, some 130 miles North West of the Mexico City. The first mine was Santa Maria del iris. Soon other mines were opened La Carbonera, La Hacienda, La Trinidad, and El Perido being but a few of the first mines. The colonial City of Queretaro became center of the Mexican opal trade. In the late 1950's Alfonso Ramirez of Queretaro discovered opal near the small town of Magdalena about 50 miles North West of Guatalajara in the state of Jalisco. He opened the first mine La Unica,close to the valcano Tequila Soon after prospectors and miners moved from Queretaro to Magdalena.and Other deposits were discovered in the municipality of Magdalena (Las Latillas, La Mora, San Simon, Las Cruces, San Martin, El Huaxical and El Cabon being but a few of the early mines. By 1960 there were hundreds of mines around the small town of Magdalena. From the early 1960's to the late 1970's much opal was produced by the mines in the state of Queretaro and the Magdalena area. No where as much mining takes place now. It seems the best deposits were discovered back then and mined out.
I remember back in the 1970's many vendors of opal in the plazas in Queretaro and the plaza of Magdalena especially at the weekend when the miners would come into town.
Back then the orange to red opal with no play of colour was generally known as Cherry opal. It was cut en cabachon and given to the women and children to get what they could for it. It was possible to sit in the plaza and buy quite a few of these stones for just one dollar.
Of course they are now almost always faceted and known as fire opal - good marketing! Mexican opal has always been much appreciated by the Germans and japanese. In 1969 Shdao Machizuki of Japan bought the San Simon mine, which is a few miles north of Magdalena. He did much to help to people in the tiny pueblo of San Simon and improved mining methods. Shdao is now retired, but the mine is now run by his son Satoshi.
The pictures below are of the Pata de Gallo mine, a few miles North West of Magdalena. It is owned and operated by Miguel Tomayo. It is an open cast mine which uses a bulldozer and a backhoe. A small charge of dynamite is often used to break up the rhyolite rock. The opal is in pockets and seams in the rock. Opal mining is a risky business. With the cost of buying and operating the heavy equipment, and paying the miners one can very soon go bust if opal is not found.
I do know that Miguel has good knowledge on opal and mining. Even so, in my day at the mine the only opal I saw was from a free lance fossicker going over the dumps of rejected rhyolite rock.
Always buy opal from a reliable source. Ask if the stone has been kept dry, most opal contains 3-10% water - though it can be as high as 20% or more It is the drying out of the stones water content that causes it to craze and crack. If the stone has been dry for 12 months or more it should be stable.
TYPES OF MEXICAN OPAL
-Precious opal: opal with a play of colour.
-Crystal opal: clean transparent opal with a play of colour
-Water Opal: Transparent opal the colour of clear water with a play of colour.
-Fire opal: Now reserved for orange to red opal with or without play of colour. Which is usually faceted
-Matrix opal : Opal in its rhyolite matrix rock. Known as cantera in Mexico (Watch out for the man made matrix. Bits of opal set in a colored cement or apoxy. This is then ground and polished into a cobochon).
-Jelly opal : A cloudy or translucent opal.
-Hydrophane : An opaque opal which when soaked in water becomes transparent.
-Common or Potch opal :Opal with no play of color.
TERMS FOR PLAY OF COLOR :
-Pinfire: Small close set patches of color.
-Harlequin: Broad angular, close set patches of color.
-Flame: Sweeping red or reddish flashes of color that shoot across the stone.
-Rolling flash: Color flashes that appear as the stone is turned.
-Opal is a hydrous silicon dioxide.
-Crystal system:None - it's amorphous.
-Hardness 5 to 6.5
-Density around 2.1
-The play of color in opal is caused by defraction and interference of light from microscopic silica spheres which opal is composed of.
INCLUSIONS IN MEXICAN OPAL
Mexican opal often has inclusions of Goethite like needles, sometimes wrapped in limonite.
Hematite crystals and botryoidal inclusions of white chalcedony. The inclusions often create amazing scenes when under magnification. Dr Edward Gubelin has taken some amazing photos of inclusions in Mexican opal.
For anyone wishing to visit the opal mines Queretaro is a nice place to stay. It is a Spanish Colonial city with lots of pleasant plazas. The center of the city is a Unesco World Heritage Site. In Magdalena the Hotel el Opalo, just off the plaza behind the church is a good place to stay. The owner Gonzalo Bonuelos has a good knowledge of Mexican opal. He is also a vendor of Mexican opal.
PHOTO: Dave Gibson at the Miguels mine
PHOTO: Welcome to Pata de Gallo mine
PHOTO: Going deep
PHOTO: The mining is open cast
PHOTO: Discussing if a rock contains opal.
It will be split open with a hammer and chisel
PHOTO: Miguel examining opal from a freelance fossicker
PHOTO: Decent quality Mexican opal
PHOTO: Matrix opal containing Goethite needles
PHOTO: Matrix Opal with full spectrum of rolling flash
PHOTO: View of Tequila volcano from Hotel el Opalo
PHOTO: Morning in Mexico
- Mexican Opal - an article by Dr William Foshag, head curator of Geology, at USA National Museum from 1953
- GARY ROSKIN : an article on Mexican opal
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