Mexican Opal Gemstone Information


Mexican Opals are known for their vivid yellow, orange or orange-red colors. The intense color has earned this gem the nickname fire opal. Unlike precious opal, the Mexican Opal does not usually exhibit a play of color. But it makes up for this with its remarkable body color. It is the few varieties of opal that can successfully be faceted, as some specimens can exhibit considerable transparency.

The prices and value of Mexican Opal vary according to the size and quality of the gemstone.  The vivid orange and red colors are the most valuable, while the paler yellow and white tend to be less expensive. Transparent specimens are rare and valuable.

Why Buy Loose Gemstones Instead of Pre-Set Jewelry?
There are many reasons, but mainly it comes down to value and choice...

When buying your Mexican Opal gemstone loose instead of a pre-set stone, you can be sure that you are getting the best value for your money.  Loose gemstones are less expensive, a better value, and you can really see what you are paying for.  The most important part of getting the right price and finding the best value is to first see what you're getting.  A jewelry setting will hide the inclusions inside a gem, and can deepen or brighten its color.  With a loose stone you can much more easily inspect the gem and see it for what it really is.  In this way you can get a better idea of its true worth and be sure you are paying a fair price.

The second advantage of buying a loose gemstone is choice.  You are free to pick the exact color, cut, shape and variety of the stone for the setting of your dreams, be it yellow gold, white gold, platinum or silver; prong set or bezel set with diamond accents.  You can experience the joy of creating your very own, one-of-a-kind jewelry design. Choose from a variety of jewelry settings and styles to create a completely original presentation that will perfectly suit your individual gemstone and will be as unique as you are!


Mexican Opal Jewelry                                     Mexican Opal Ring



Origin The major source is Mexico, but also found in small amounts in South America and the United States (Idaho and Oregon)
Color Fiery red, yellow, honey and orange hues.
Refractive Index  1.37 - 1.40
Chemical Composition SiO2·nH2O
Hardness  5.5 - 6.5
Density  2.10
Crystal Structure Amorphous
Month October
Zodiac Signs Libra, Scorpio and Aries


Natural Carved Mexican Opal                           Fire Opal from Mexico


Mexican Opal is considered a mineraloid and has no crystal structure. The term used for no structure is amorphous. Opal is scientifically written as SiO2 NH2O or hydrated silicon dioxide.  Opal typically contains a significant water content. Stones that can commonly form Opal are limestone, basalt, rhyolite and sandstone. While Opal contains water, the water content does vary by stone.  For instance, Opal has been found with water content approaching 20%, however, most Opal stones used for ornamental jewelry usually have water content of 3% to 10%.  Fire opal, like all opal, has a high water content. As a result, it should be protected from heat and prolonged exposure to strong light, which could dry it out. Dealers cure fire opal by drying it before cutting to make sure that any instability can be eliminated. Still, all opals need to be handled with care.

Mexican Opal is rated at 5.5 to 6.5 on Moh's Scale of hardness. The physical structure of Opal is unique. Tiny spheres of silicon dioxide form a pyramid shaped grid interspersed with water. Tiny natural faults in this grid cause the characteristic "play of color" - opalescence. The effect is similar to the rainbow colors displayed on a soap bubble, only much more dramatic.  The incredible play of color is exhibited by the gemstone due to the presence of small spheres in the silica gel that causes interference and refraction appearance. Silicon and oxygen chains are packed in the spheres and these are uneven in size and incoherent in concentration. These are set in a compact structures thus, when ray of light falls it dissects the light on its way through the stone resulting in the awesome color play. As per the size of the spheres within the structure, changeable colors of the gamut are diffracted. With the increase in the consistency of the spheres position, more intense and brilliant would be the color play. 

Mexican opal that displays play of color but is rare because volcanic opal forms relatively quickly and the spheres of silica rarely have time to settle into the diffraction grids that create play of color.

Mexican Opal has a refractive index of 1.37 - 1.40 and a vitreous to resinous surface luster.  The refractive index (RI), measured using a refractometer, is an indication of the amount light rays are bent by a mineral.  Birefringence is the difference between the minimum and maximum RI. When birefringence is high, light rays reflect off different parts of the back of a stone causing an apparent doubling of the back facets when viewed through the front facet. 

Most gems have a crystalline structure. Crystals have planes of symmetry and are divided into seven symmetry systems. The number of axes, their length, and their angle to each other determine the system to which a crystal belongs.  Mexican Opal crystalizes in the amorphous crystal system (trigonal-trapezohedral), without a particular crystal habit.


Fire opal glows with the fire of the sun: hot honey yellows, oranges, and reds so bright they look as though they might glow in the dark. Fire opal sometimes only occasionally exhibits an opalescence or play of color like other opals but it does not need this to take a starring role in jewelry. Its juicy color is just the right accent to earth tones or black and also looks great paired with other bright tones.


Fine Opal stones are cut and polished to round or oval cabochons or other softly domed shapes so as to display the best color. First, the cutters remove the inclusions present in the stone with a diamond cutting wheel.  Next a soft dome shape is given in order to bring out the fine color play. After cutting, the finishing is done using sandpaper, and finally the polishing is done with the help of a wet leather wheel. Jewelry designers can get many desirable cuts or the shapes from this striking stone. Oval, circular and round cabochons are preferred as in these shapes the color play is displayed at its best. Some other popular shapes are teardrop, square, rectangle and triangle etc. 

Unlike most opal, fire opal is sometimes faceted, so you can choose sparkle as well as color. Because it is light as well as bright, fire opal is especially good for earrings, where even small sizes have a big punch of color.  Only the very finest qualities of Fire Opal are suitable for faceting. 



Opal is a soft stone and therefor is occasionally treated or impregnated with colorless oils, plastic, resin or wax which act as a bonding agent, reduce the visibility of the inclusions and improve the overall clarity of the stones. Black Opal is occasionally treated with chemicals, smoke, or dye.  Opals are alsio sometimes backed with foil, black paint or laquer.  Thin opal is often made into doublets, or triplets by covering the back and front. 

AJS Gems fully discloses any and all treatments to our gemstones.


Opal began its formation 15 to 30 million years ago, during the tertiary period. Starting out as a liquid, the slurry seeped through sedimentary layers of earth, settling within impervious clays at a depth of 20 to 30 metres. Over the coarse of millions of years, the liquid slurry crystalized, becoming precious opal.

Mexican Opal was born in fire, in the ancient volcanoes of Mexico. Fire opal forms when water seeps into silica-rich lava, filling seams and hollows. Under heat and pressure, the silica forms a solid gel, trapping the remaining water within its structure. Small pebbles of fire opal are found embedded in lava flows.


Mexican Opal Mine


Fire opal is found in Central America, South America and the United States (Idaho and Oregon), typically within cavities formed in volcanic lava flows.  The vast majority is from Mexico.  Mexican opal is mined in the Mexican states of Queretaro, Hidalgo, Guerrero, Michoacan, Julisio, Chihuahua and San Luis Potosi. The most important mines in Queretaro were discovered in 1835 and are still producing today.



Opal is derived from the Latin word 'Upala' and the Greek word 'opallios', both meaning “precious stone”.

The Roman scholar and famous author Pliny once described Opal as a gemstone that combines the best possible characteristics of the most beautiful of gemstones: the fine sparkles of Almandine, the shining purple of Amethyst, the golden yellow of Topaz, and the deep blue of Sapphire, “so that all all colors shine and sparkle together in a beautiful combination.”

In Greek mythology, Opal was believed to be formed from the joyous tears wept by Zeus after he defeated the Titans. It was also believed by the Greeks that the owner of Opal would obtain the power of giving foresight and the light of prophecy.

In ancient Arabic times it was believed that opals fell from the heavens in lightning, the flashes giving the stone its fire and flare.

It is said that Opal was part of Cleopatra's famous jewelry collection, and that she used the stone to attract the attention of Mark Anthony.

Opal is said to be a symbol of faithfulness and is believed to assist the wearer with finding true love. Opal is also believed to cure depressions and bring confidence to the wearer. Opal helps to open unused parts of the mind in order to increase creativity and mental capacities.

In past, it was believed that wearing this fascinating gem helps in finding the true love. Also it was considered as an icon of faithfulness and confidence.

Women in ancient times used to wear opal to protect their hair from graying. It was largely used for ritual magic.

Astrologers recommend different opals for different zodiac signs. Black Opal favors those having the Scorpio zodiac signs while Boulder Opal suits for those having Aries as their sun sign.

Opal helps in overcoming depression in life and diverts the energy in improving the positive traits. It enables the wearer to use his/her brain fully.


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