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Opal

“The fire of opal is soft and gentle, and with a purple hue as amethyst and green sea as emerald: everything blends together in brilliant splendor" - this how Pliny the Elder describes this wonderful stone.

opal many stones

Its name is derived from the Latin word opalus which literally means “enchanting the sight”. According to another theory the name comes from the Sanskrit word “upala” and means precious stone. It is one of the most mysterious gems. Since ancient times it never ceases to fascinate people and in times its popularity experienced ups and downs to be back on the top today.

The most amazing quality of opal is its ability to refract and reflect light in a specific way. This quality made it one of the most wanted and popular gems of all time.

opal transparent crystal
opal crystal

Unlike minerals which form crystals opal is amorphous. Actually it is not classified as mineral but mineraloid form of silica. It is chemically similar to quartz but contains from 3% to 21% water in its mineral structure. Clean opals usually contain between 6% and 10% water. It is the most phenomenal stone in the world but its water content and relative softness makes it very sensitive, requiring special care and attention by its owner.

There are three main varieties of opal:
common opal - usually opaque to translucent, without play of color

fire opal - so called for a predominantly yellow-orange-red range of colors. Usually it does not show play of color. Fire opals of highest quality are transparent and clear, suitable for faceting.

fire opal

precious opal - most interesting feature of this type of opal is the play of colors, i.e. flashing in different colors of the rainbow when changing the viewing angle. The most rare and highly valued are black opals, a very dark grey and blue, almost black in color.

Common opal

commoon opal

Precious opal

precious opal

The play of colors seen in precious opal is explained by the arrangement of microscopic spheres of silica in different parts of the stone. These stacked structures of micro-spheres act as a diffraction grating and decompose white light. Observed colors in their "game" are depending on the size of these micro-spheres. As the arrangement and orientation of the field is not uniform and the game flashes of color are unevenly distributed in the volume of the stone.

In the play of colors of the precious opal most common are blue and green, and the rare - red. Accordingly this significantly affects the price of the stone and those having more red in the play of color are most valued. The quality of precious opal is considered excellent if the play of color is visible at daylight from a distance of 60-90 cm.

opal cabochons and crystal
opal pear shaped

Some precious opals are sensitive to rapid change in moisture and can crack on the surface or inside. This process is unpredictable and is associated with rapid drying of opal. This could be caused by the heating during the cleaning and sanding or mechanical vibrations in the stone treatment. High quality rough opals are often stored in water. The process of their preparation for mechanical treatment (drying slowly) can take several years. This reduces the likelihood of cracking.

Very often precious opals are produced in gems as doublets or triplets. Doublet is a thin plate of opal over a base of dark material (low-quality opal, obsidian, basalt). The dark base enhances the play of colors. This technique also allows doublet opal to achieve the effect of the black opal and the jewel is at much lower price. There are also opal triplets which have their top covered usually by clear quartz or plastic. Thus they are protected from mechanical damage and cracking.

opal
opal

Opal has been imitated since ancient times. Most often it were glass imitations than natural stone, but still more expensive than imitation glass.
Opal with play of color was first created in a lab in the early 70s. Now there are several techniques for its preparation. Usually the process takes months and even though lab opal is much cheaper.

Preservance

Natural opal is very picky gem and should be kept away from heat, prolonged exposure to bright light, shock, pressure, acids and bases. It is not recommended to clean opal by steam, ultrasound or chemicals.

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