There’s no doubt that Mardi Gras is a colorful celebration. Although the ‘official colors’ of the celebration are purple for justice, gold for power and green for faith, every color of the rainbow can be seen in headdresses, costumes, masks, and banners on the streets of New Orleans.
So it is appropriate that the Louisiana opal, which is composed of quartz, opal, and pyrite, is an iridescent, and sparkly gemstone that offers the rainbow’s full spectrum after it is polished. But you will not see an abundance of those precious gems at Mardi Gras. The basal Fleming Formation of Vernon Parish, Louisiana, near the Texas border was the only significant mine that produced the gem. And since the mine shut down more than a decade ago, all that was mined then is all that exists.
An article titled A California Yankee in King Cake’s Court, explained how these gemstones are formed:
Louisiana opals occur when the opal matrix forms inside of quartz sandstone. They are considerably harder and less brittle than fire opals or black opals, and so can be cut in large cabochons and set without a protective backing. They are less gaudy than other kinds of opals, appearing to be merely a piece of polished beige-grey sandstone–until you turn them, and green, blue, purple, teal, gold, and aqua flashes out at you. There was only ever one commercial mine for them, the Hidden Fire Opal Mine in Vernon Parish. It was operated on land owned by Boise Cascade, which shut it down after just four years because they figured the timber was worth more than the opals.
According to an article in Geology.com…
“Small amounts of a material called “Louisiana Opal” or “Louisiana Sand Opal” have been mined from the Catahoula Formation near Leesville, Vernon Parish, Louisiana. If you examine this material closely, you will find that it is sandstone in which the sand grains are bound together by a cement of clear precious opal.
When this sandstone is completely cemented, solid, and unweathered, it is stable enough to be slabbed, cut into cabochons and polished to a bright finish. When a polished cabochon is played in incident light, the interstitial opal can produce small patches of play-of-color.
… It is a novelty gem that is enjoyed by local people and gemstone collectors.”
In 2010, one of the rare opals could be seen at a Louisiana gem and mineral show.
Usually, when gems are scarce, they are more valuable, and also tend to be counterfeited or even just copied. We haven’t heard of any Louisiana Opals being manufactured. Synthetic gemstones are created in a lab but have the same chemical and physical properties as real gemstones. Simulants resemble gemstones but have different chemical and physical properties. Precious gemstones are valued according to color, cut, clarity, weight, and in some cases country of origin. We wrote about how FT-IR spectroscopy can detect treated gemstones in Is It Natural or Man-made? Detecting Treated Gemstones.
Another technique that can screen gemstones is Raman spectroscopy, which is non-destructive, requires almost no sample preparation and is exquisitely sensitive to crystalline structure and the presence of minor components. For these reasons, Raman is becoming widely recognized as a valuable tool for the analysis of gems and minerals. For high value gemstones, Raman spectroscopy is able to distinguish between genuine and fake specimens and determine whether stones have been artificially treated with high temperature or pressure or with fillers and waxes to enhance their color and raise their value. (You can read more in Rapid Screening of Semiprecious Gemstones by Raman Spectroscopy.)
We haven’t heard of any synthetic Louisiana Opal, but if you see any of these gems being thrown from floats down the streets of New Orleans, most likely they are not the real thing.
Editor’s Note: Mardi Gras 2016 falls on Tuesday, February 9.
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