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Home Precious stones Opal

Opal

opalThis stone is known to virtually everybody. But though its name coming from Latin opalus or even more ancient Sanskrit upala means “precious stone,” though sadly, this gem is not considered precious as it occurs much too often in nature to earn that distinction.

Opal consists of silicon oxide (5-10 percent) and molecules of water SiO2+H2О; Moh’s hardness is 6.5. A major peculiarity of this stone is that it has no crystalline texture. Instead, opal has a special “superstructure” of its own, consisting of particles of silicon oxide that are aggregated into minuscule spherical arrangements. These arrangements are of different sizes and found in a rather chaotic layout in ordinary opals. As for the noble opals, these arrangements are more ordered, so such stones have a very important feature: color play. This wonderful effect is called opalescence, which makes a stone look like it is crossed by brightly colored clouds.

But this is not the last division in the opal classes. Though noble oplas are used in the jewelry, not all of them are valued highly. As far as price, only one variety of opal equals that of precious stones: black opals. A stone the size of a finger could easily cost up to $50,000. Moreover, black opals have the brightest opalescence of all. White opals probably have the same level of opalescence, but it vanishes on the pale background.

Most opals are found in Australia. A million years ago, a part of this territory was covered with the waters of an interior sea. Over the years, the sea dried out, and as the water receded, the particles of silicon in the earth filled the cracks and holes in the rock. As these elements dried out, they gradually formed what we now know as opal. So we may say that the opals’ wonderful shine and pattern is what the waves of the ancient sea used to be.

Pink gold rings featuring a pink opal and brilliants Pink gold rings featuring a pink opal and brilliants Opal escenceOpal escence Pink gold brooch-pendent with a carved pink opal, pearl, sapphires and brilliantsPink gold brooch-pendent with a carved pink opal, pearl, sapphires and brilliants

People discovered Australian opal only in 1849, when a deposit as found on a cattle farm in Tarravilla. In due time, all the major Australian deposits were developed: White Cliffs, Lightning Ridge, Andamooka, and Coober Pedy. These deposits are where the best opals are mined. Coober Pedy is from the aboriginal language and means “white man sitting in a hole.” This name is appropriate; all work at the deposits was carried out in the most primitive way. A pickaxe and a spade were used to dig holes of 5 meters and over and the rock was removed in buckets, as the miners tried to cover themselves from the heat and brisk wind.

However, this stone is found not only on the Green Continent. Opal is known from the earliest times and was described even by the Roman historian Pliny: “It has the softness of a ruby’s fire, the brightness of a lilac amethyst and the sea green of an emerald. This combination creates the wonder we call opal.” The Romans mined this mineral in the Carpathians. In the Middle Ages, opal was called the “eye stone” due to its reputation to positively influence the eyesight. Some thought that those who wore opal would become invisible, which is why this stone was especially popular among thieves.

Napoleon once made a wonderful gift to his beloved Josephine: a fantastic fire opal called “Burning Troy.” Unfortunately, the Emperor failed to see the fire of Moscow in this opal, the one that burned down to ashes his own glory and power. If he had better foresight, everything would have eventually turned out better for both him and Moscow. However, this stone now would cost a great deal only because of its famous owners. Prices for fire opals are now extremely low, and some gemologists even refuse to classify them as noble opals.

Opal gained its popularity due to Sir Walter Scott, a writer who once depicted a wonderfully strong woman whose life power depended on the opal stone she wore in her hair. It came to no good, though; when the internal fire of the stone went out, the woman died. That is why the popular belief then appeared that opal could bring bad luck to its owner.

Opal set in a pieceOpal set in a piece opal_06 Black opalBlack opal

The popularity of opal is attributed also to a real woman: Queen Victoria of England, who was ruler of Britain in the 19th century. For the English, Victoria became a very important figure, as a whole era was named after her. It was during her reign that in Australia the first black opals were found, and Queen Victoria helped promote this stone. At that time, the Green Continent was known only as Botany Bay, and Britain sent its convicts there. So the Queen decided to help repair the image of this colony and helped to associate Australia with a beautiful stone rather than with any penal servitude. Victoria began to wear jewelry with black opals, and gave them to her daughters and her confidants as wedding gifts. Her plan was successful; black opals became fashionable and, subsequently, very expensive.

Black opal, however, is not always exactly black. Black is the color of the rock, its backing. The most exciting feature of this gem is that it can play becoming orange, bluish, reddish, golden, lilac, or even silverygreen (the last two variants are the most widespread). Only very few stones have the black backing. Such opals are the most valuable, but even in Australia, most of the stones have a dark gray or even light gray backing.

Opals are usually given a cabochon cut. When processing a stone, it is very important to keep it cool, as heat will spoil this gem. Just the same, it is recommended that you keep your opal jewelry far from sources of heat, otherwise the stones might lose their color play. It would be possible to restore the color only in a vacuum installation. The major problem of black opals is their spontaneous cracking. That is why when buying opals, always ask if they were subject to any stabilization. To improve stone’s play and hide the cracks, opal is often treated with all kinds of oils and waxes, though such treatment considerably lowers the price.

White opalWhite opal opal_07 Mexican fire opalMexican fire opal

As the large quality opals are quite rare, these gems are often used in doublets and triplets, with opal set on some other backing. For the best color play, opal should show on a black background, so when making doublet a black mineral, such as black obsidian, is usually used. But the most valued combination of all is the natural one that is called boulder opal, a film that opal formed on the mother rock. Such stones are sometimes even more expensive than homogenous opals. The triplet also has a clear capping, some transparent mineral which should protect the delicate opal from the aggressive influence of the environment.

The best black opals are now mined in Australia; also there are deposits in Brazil, Mexico (opal was widely used by the Aztecs), and the U.S. Today, the development of deposits in Ethiopia and Mali have also begun.

It is to be noted that the play in any noble opal should be seen in the normal light from at least 60 cm, or even better, 1 meter. If you cannot see such effect, then this black opal belongs to those precious stones, which are sold by weight.

As the price depends on the color play, its perception is always very subjective, and the assessment of value, even by qualified experts, may have quite a large margin. The principle is simple: opals with red and yellow sparkles are valued more than those with only blue and green sparkles. Some years ago in America, there was an interesting experiment. An opal ring was presented in turn to some respectable jewelry companies. The minimum price named was $200 and the maximum was $5,500—quite a range for this stone.