In Twelfth Night Shakespeare referred to opal as "the queen of gems." The name Opal was probably derived from Sanskrit "upala", meaning "valuable stone". This was probably the root for the Greek term “opallios”, which translates as “colour change”. Later, the Latin word "opalus" came to mean precious stone.

Most opal is 50-65 million years old, dating back to the period when dinosaurs roamed the earth.

Opal is the most colorful of all gems. Its splendid play of color is unsurpassed, and fine examples can be more valuable than diamond.

Opal is an amorphous form of silica, (SiO2.nH2O) chemically similar to quartz, (SiO2) but containing 3% to 21% water within the mineral structure. Gem grade opals are usually 6% to 10% water content.

The play of color consists of iridescent color flashes that change with the angle at which the stone is viewed. The play of color may consist of large, individual flashes of color (known as schillers), or may be of tiny, dense flashes. The intensity and distribution of the color flashes is a determining factor in the value of an opal.

There are two distinct types of opal, common and precious. The way the silica particles form determines which type. In precious opal, silica particles are packed in regular rows and layers, where as in common opal they are hazily arranged.

Opals displaying play of color are known as precious opals, and opals lacking play of color are known as common opals. Light opal is the most common type of opal found and refers to both the crystal type opal (translucent) and the milky opal (opaque). It is the most common variety and is generally less valuable than gem quality light opal. Brilliantly colored light opals may be quite expensive with a value exceeding some Black and Boulder Opals.

White Opal - Opal with a light colored body color (white, yellow, cream, etc.) with strong play of color

Fire Opal - Mexican fire opal, a transparent to translucent orange red form of common opal. If Mexican fire opals display play of color, they are known as Precious Fire Opal.

Black Opal - The most desired and beautiful form of opal is black opal. Black Opal comes from the Lightning Ridge region of Northern New South Wales . It is the most rare and most valuable opal. Fine quality black opals often cost more per carat than diamonds. The term black opal is misleading because the opal is not actually black, but instead has a very dark base, which is opal with a dark blue, dark green or black background with a strong play of color.

Crystal opal - transparent to semitransparent, colorless body with play of color.

 Boulder opal - a thin seam of precious opal on ironstone matrix. Since this is a natural occurrence, its value is higher than that of a man made doublet. The ironstone is very dark, which makes the fire stand out and gives a close resemblance to black opal

 Matrix opal – consists of thin seams or spots of precious opal in matrix. The matrix is usually dark ironstone, but occasionally a light sand stone. Also called Mass opal.

Gems are cut from both the precious and common forms, but precious opal is the primary gem form of this stone.

n order to best bring out the play of colour in an Opal, the stones are cut and polished to round or oval cabochons, or any other softly domed shape, depending on the raw material. Only the best qualities of Fire Opal, however, are suited to faceting.

Opal is often found as flat lenses, or thin layers, bigger pieces are rather rare.

If you leave a thin but supporting layer of the harder mother rock, you will receive a pre-stage of the Opal-doublets which are frequently used today for mass produced jewellery. These are gemstone combinations consisting of a surface from millimetre -thin Opal plates, which have been mounted on Onyx, Obsidian, artificial black glass, or Potch-Opal. Triplets have been developed from this design; here the Opal layer receives an additional cover from Rock Crystal, Plastic, Hard Glass or Lead Glass for protection.

 Doublets and Triplets make use of opal that is too thin to use as a solid gemstone.

1. An "opal-triplet" is made up of three sections, a (top) polished quartz cabochon to protect the opal layer, a center opal slice, and a bottom piece of "potch" or dark material to provide strong contrast for the center slice of opal, and protect the rear of the stone. The contrast of black as seen through a thin slice of opal makes it look like the highly prized "black-opal".

2. An "opal-doublet" is similar to a triplet, but has only the polished quartz top and the slice of opal. It does not have the backing material. As a result the slice is usually thicker, and the stone takes on more of the characteristic background color of the original opal.

In 1964 after it was revealed that opal is made up of spheres of silica. Mr. Pierre Gilson synthesized both white and black opal and in 1973.

Synthetic opal first came on the market in 1974 and has been improving ever since. A skilled gemologist can distinguish it from natural opal by viewing it under magnification, but to the untrained eye it looks natural.

Opal has been duplicated in the laboratory, and the material provides a very close approximation to the natural material. It is produced by the controlled (very slow) precipitation, and alignment of small silica spheres. The spheres form a three dimensional diffraction pattern which produces the color play.

Under U-V (particularly L.W.), the Gilson opals show a distinctive chalky bluish-white body glow and a much stronger surface fluorescence of the same colour.

When viewed under high intensity fibre-optic illumination, a "chicken wire" structural effect can be seen. Under normal illumination, the typical "lizard skin" structure present in both black and white

Beside synthetic opal there are also some opal "simulants" on the market. A simulant is something that resembles the natural material, but is composed or produced in an entirely different way.

One such simulant is "Slocum Stone", a scientist from USA Dr. John Slocum surprised everyone by producing an extremely realistic imitation also known as “Slocum Stone” it appears to be a type of glass

It is harder than opal and much more durable, and does not appear to be affected by heating like true opal.

he color display is similar under close up, but it tends to look more transparent than the colors in the natural stone.

Most Precious Opal is mined in Australia , the U.S. , and Mexico . Some of the most famous Opal deposits are in Australia , Andamooka , South Australia Coober Pedy , South Australia
Lightning Ridge, In Mexico, Precious Opals and Fire Opals come from several deposits. The U.S. has some of the most outstanding Opal occurrences producing all types of Precious Opal.

Opals are generally stable to light, but heat from intense light can cause fracturing (known as "crazing").

A condition called crazing affects certain opals, causing them to form internal cracks. Crazing is a particularly interesting phenomenon, for it lacks consistency and is unpredictable. Although it can occur at random, it usually strikes when an opal removed from damp conditions is allowed to dry too quickly, or when an opal is exposed to sudden intense light -- or a combination of these factors. Crazing may also take place when an opal is subject to vibration, as during the cutting and polishing of a specimen. The severity of the crazing and the time it takes to "craze" varies among specimens. The origin of the specimen is often a determining factor to its resistance to crazing.

Opals are attacked by hydrofluoric acid and caustic alkalis.

Loss of moisture, and crazing, can result from storage in airtight containers, such as safe deposit boxes