Opal is a noncrystalline form of the mineral silica which, despite its amorphous structure, displays an amazing degree of internal organization. Opal is related to its more commonly found but highly crystalline cousins quartz and agate, and is formed from amorphous "balls" or "lumps" of silica rather that from ordered, naturally faceted crystals.

The chemical composition of opal is SiO2H2O, silicon dioxide combined with water (an opal stone may contain up to 30% water.) The silicate minerals in the stone add to its weight, giving it a specific gravity ranging from 1.98 to 2.5 times that of pure water. Opal's scratch hardness is measured at 6.0 to 6.5 on the Mohs' scale, similar in hardness to quartz, a little more than halfway between the hardness of talc and diamond.

Most opal is more than 60 million years old and generally dates back to the Cretaceous period when dinosaurs roamed the earth.

It is found near the earth's surface in areas where ancient geothermal hot springs once flowed. The minerals bubbled up from beneath the surface of the earth and slowly, over the centuries, lined the walls of cracks, vents and underground cavities in the bedrock. Most opal is found where geothermal hot springs dried up during seasonal periods of rainfall and extended dry periods.

More than 90% of the world's quality gem opals come from Southern Australia, although it can be found in other parts of the world such as Brazil, Mexico, Czechoslovakia and Nevada. All black opals (see below) come exclusively from Australia.

The story of opal in Australia begins more than million years ago when the deserts of central Australia were a great inland sea, with silica-laden sediment deposited around its shoreline. After the sea receded and disappeared to become the great Artesian basin, weathering 30 million years ago released a lot of the silica into a solution which filled cracks in the rocks, layers in clay, and even some fossils. Some of the silica became precious opal. Opal is one of the few gemstones that is sedimentary in origin. The water in opal is a remnant of that ancient sea.

The most striking quality of opal is its ability to refract and reflect specific wavelengths of light. In fact, the term "opalescence" was coined to describe this phenomenon. The size and spacing of the amorphous spheres of silica within the stone refracts specific wavelengths of light; each sphere refracting a single, pure spectral color much like the individual microscopic droplets of water in a rainbow. The interplay of these pure wavelengths of light gives opal its unique visual appeal, and makes it one of the most sought-after gemstones in the world.

Preservation and Handling of Opals

• Opal is a "living" stone, which means it must be protected from heat and detergents that "dry" the gem.
• Opals develop crazing if they are allowed to dry out.
• Heat treatment is catastrophic!!
• In addition to cracking, loss of water causes loss of iridescence. 

Working with gem-quality Opals

Care must be taken when polishing and setting opals. Despite their hardness, they are prone to crazing and cracking, and loss of water content causes a noticeable loss of iridescence. To prevent this, opals are normally stored in moist cotton wool or cloth until it is time to work with them. Sometimes, an opal that has lost its opalescence may be "rejuvenated" by rehydrating the stone with water or special oils, but this may only temporarily improve the stone's appearance.

In the opal cutting process the potch (a kind of mineral crust) is ground away from the presentation areas of the gem opal. This process unlike diamond mining, where the blueground (Kimberlite) is crushed away from the diamond crystals.

Individual opals are "dopped" -affixed to the ends of wooden dowels about the size of old fashioned wooden clothespins, usually with dopping wax, which resembles sealing wax.

Grinding and polishing of opals is done under a cold water drip to prevent the stones from overheating and cracking. A series of grits is used, from coarsest to finest, to produce the desired finely polished surface that reveals the full play of color in the opal.

Most gem opals are ground to a highly polished convex oval shape called a "cabochon."

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Types of Opals

Boulder Opal | Common Opal | Crystal Opal | Fire Opal | Gem Opal

 

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Gem Opal	Precious opal, which displays "opalescence" (spectral color, iridescence that changes with the angle at which the gem is viewed), is the kind of opal with which most people are familiar. There are three major kinds: White Opal - White opal is an opaque stone in which the colors appear as flashes or speckles. Black Opal - Black opal contains fire with a dark body color. These are less common and tend to be costly. These are the investment high quality opals ! Opalized Organic Material - Opalized organic material may consist of wood, plant stem, bone or shell that has been petrified under extremely rare conditions.
Crystal Opal	Crystal opal, the next most costly type of opal, is transparent with flashes of color. It is highly valued for the brilliance of its colors and the fact that many layers of color can be seen within the stone.
Boulder Opal	Another unusual type of opal is boulder opal, which has opal with an ironstone host rock matrix which creates a natural dark background to view its fire. These sometimes occur in "splits," a matched pair of opals created when a price of boulder opal is split along the opal vein. These are particularly favored for earrings, since they are mirror images of each other.
Fire Opal	Fire opal is transparent or translucent with an orange or red body color. Fire opals are named for their reddish color but are opalescent. Be careful not to misinterpret the term "fire" as iridescence, because in precious opal (with a play of iridescent color) the play itself is also called fire. Much of the world's fire opal is mined in Mexico.
Common Opal	Common Opal is rather opaque with no spectral play of color. Many names are used to describe common varieties. Among these are honey opal, milk opal, and moss opal. Examples include milky agates and certain "petrified" opals.

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Evaluating and Purchasing Opals

Evaluating opal quality is a specialized business. It is difficult for the average person to tell the difference between a moderately valuable stone suitable for a ring or a pendant and an investment grade black opal worth as much as $20,000 per carat. In addition, the buyer must beware of the relatively recent appearance of "created" or synthetic opals, and of "manufactured" opals that consist of thin layers of true opal material bonded together to make a more substantial gem. Some unscrupulous gem sellers have even gone so far as to grind inferior opal material and mix it into a clear epoxy resin, which is then cast into the traditional cabochon shape.

With these caveats in mind, in general, when you see a stone you like, buy it. Some factors you can consider in evaluating its quality are the play of color, its "fire," "sparkle" or intensity, the rarity of the color or colors, and how "directional" the colors are.

Evaluating Quality
Intensity	The finest gem opals look like someone has turned the color knob all the way to the right. There's nothing subtle about them. They flash and flare and seem to glow with a mysterious inner fire, even in indirect light. One way to spot the most intense stones in a tray of opals is to squint at them and see which ones "pop" out from the rest. (An aside: one of the worst ways to view them is in the harsh halogen lightning of your typical "mall" jewelry store.)
Color	Color in opals ranges from the finest milky white to a beguiling azure-green to the rarest and most expensive opal of all, a deep, red-flecked black. Red in any opal is an indication of quality, and therefore greater worth. the iridescent red flecks in most gem-quality opal is also an indication of "fire" or "pinfire," a common measure of an opal's worth. For those who are interested in a pleasing piece of jewelry rather than investment, color preference is a matter of personal choice. In that light no single color is better than another.
Direction	An opal has a definite "direction." The finest opals will show a bright play of color across the entire stone no matter how the stone is viewed. Others may display their colors only when viewed from certain angles. Still others may display their colors from a single viewing angle. In general, the narrower the directional the play of color, the less valuable the opal. The presence of potch - opal that has no play of color, usually white, gray or brownish - on the surface of the opal reduces its value for the same reason, lack of appearance of direction.
Opal Doublets and Triplets	If you are on a limited budget, consider an opal doublet, which is an assembled stone with opal on top and another stone, usually obsidian or ironstone, laminated to the back. These are produced to take advantage of high quality opal material that is too thin to stand on its own. Because there is less gem opal involved, they cost a lot less, and the dark background really shows off the play of color in the opal. A high quality doublet will give you the look and beauty of a fine black opal at a fraction of the cost. Opal tripletts of the black Opal variety have a quartz cover, a thin slice of Black Opal and a basalt or black onyx bottom. The three layers hence "Triplett" are combined with epoxy. Thus tripletts are less money than any other natural Opal product. In the past, Tripletts had poor glue technology and thus could cloud up easily after continued exposure to solvents or detergent water. Our Tripletts are guaranteed not to seperate for life as per the care information located on Care and Feeding of your Opal. Tripletts offer a big Opal look for a limited Opal budget and are especially good for people who want a Black Opal look but can not afford a Black Opal.
Synthetic Opals	There are several manufacturers that make synthetic opals, including Gilson Opal, Inamori Opal. In general, synthetic opals look too good to be true, with exaggerated fire and iridescence, and a consistency from stone to stone that nature could never duplicate. I have seen tennis bracelets costing upwards of $1,000 made entirely from synthetic opal, and every stone looks exactly like its neighbor. Quite good, in fact, but by their very consistency they betray their synthetic origin. this may be for you, but nature is quite a bit more canny than the most sophisticated laboratory man can devise no two natural opals - unless cut from the same stone - will look the same.
Opal Enhancements	Opals can be enhanced by treating them with certain substances and processes. They may be impregnated with plastic or epoxy, surface oiled, soaked in sugar-rich solutions in a sulfuric acid bath to bring out a peppery pinfire effect, or heated in paper or manure to leave a deposit of carbon below the surface. All of these enhancements are temporary, and will not increase the value of the original stone. some of them lead to detrimental effects such as low specific gravity, high porosity, and increased brittleness. Beware anyone who admits to treating stones in these ways, as they are misleading and ultimately damaging to the stone.

Opal Lore

• High quality opal is more valuable than diamond; up to $20,000 per carat.
• Opal is the October birthstone.
• Some people think the opal is bad luck when worn if it is not your birthstone. This is not true. The story was started by Sir Walter Scott in his novel Anne of Gierstein, in which the heroine of the novel has her life force caught in the beautiful opal she wears and she dies when the fire in the opal is extinguished.
• In ancient times opal was accepted as a symbol of faithfulness and confidence.
• The name "opal;" is derived from the Latin word opalus, meaning seeing jewel.
• The Arabs believed that opals fell from heaven in flashes of lightning, and that's how they received their fiery color.
• Opals are very powerful in ritual magic. Since a quality opal contains every color of every other birthstone, it can be used or charged with all the energies and powers of the other stones combined and can be used in place of any birthstone for spells, rituals or other magical needs. Opals have been linked to invisibility and astral projection. and have been used to recall past lives (each color supposedly represents a past life).
• It has reputed healing properties, especially to increase mental capacities such as creative imagination and other unused powers of the mind.
• Fire opals are often used in money rituals to draw funds to those who are in need, normally worn as a pendant on a gold necklace, one surrounded with 10 or 12 small diamonds is said to have excellent money drawing power.
• Black opals are the tools of choice for witches and magicians, who use them primarily to enhance their magical receptive or projection powers. Black opals worn near the heart on necklaces made of gold are said to ward off evil, protect one from the evil eye and protect travelers on journeys to far away lands. Opals have been ground up and used a magic potions to heal the body, ward off bad dreams, and used an energy enhancement tools.
• The white opal, when used in rituals on the full moon night, is said to bring the moon goddesses' powers to full fruition in the practitioner.
• Archaeologist Louis Leakey found six thousand year old opal artifacts in a cave in Kenya!
• The Aztecs mined opal in South and Central America.
• Opal was also treasured in the Middle Ages and was called ophthalmios, or "eye stone," due to a widespread belief that it was beneficial to eyesight. Blonde women wore opal necklaces to protect their hair from losing its color.
• A beautiful opal called the orphanus was set in the crown of the Holy Roman Emperor. It was described "as though pure white snow flashed and sparked with the color of bright ruddy wine, and was overcome by this radiance."
• Opals are also set in the crown jewels of France. Napoleon gave Josephine a beautiful opal with brilliant red flashed called "The burning of Troy," making her his Helen.

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