Opal is a gemstone that combines the best possible characteristics of the most beautiful gems, "for in them you shall see the living fire of ruby, the glorious purple of the amethyst, the sea green of the emerald, all glittering together in an incredible mixture of light." This was the opinion of the famous Roman writer Pliny, who recorded his observation of gemstones for the benefit of posterity in 55 AD in his book on natural history.

      The Romans established opal as a precious gemstone, and got their supplies from traders in the Middle East. In fact, they ranked opal second only to emeralds, and carried it as a talisman for good luck, because they believed that like the rainbow, opal too brought good fortune. It is said that a Roman senator by the name of Nonius actually chose to go into exile rather than sell his precious opal to Mark Anthony who wished to present it to Cleopatra.

  
 
 
   
      The name opal itself is said to derive from one of two roots: either the Sanskrit word 'upala' meaning valuable stone, or the Greek term 'opallios', which essentially means colour change. From this, one can surmise that opal has a long and ancient history. While it is true that opal was known in ancient times, its widespread use however, only came after the beginning of the 19th century when viable deposits of the stone were found.
     
      Again, just because abundant quantities of the gem were only found as late as the 19th century, it does not mean that it was not available at all. In fact, its rarity made it all the more precious. Shakespeare is said to have referred to opal as a 'miracle' and the "Queen of Gems" and the Elizabethans as a whole prized the gem as highly as diamonds for their brilliant play of colours and flashes of fire. Some even considered it a lucky stone.

      By the late 18th and 19th centuries though, its status changed from a talisman for good fortune to the harbinger of ill luck and it was associated with famine, pestilence and the fall of monarchies and accordingly shunned. While the Black Death (plague) was ravaging Europe, there was a widely circulated rumour that an opal worn by a patient was aflame with colour while she lived and then lost all its brilliance once she died.

  
 
 
 

 
 (1) King Alfonso XII of Spain is said to have succumbed to the opal's curse.        (3) Opal mining in Lightning Ridge, Australia.
 (2) It was Queen Victoria's love for this gem that resurrected opals' popularity.     (4) Various kinds of black opals.

 
 
      Its association with the fall of dynasties probably comes from the story of King Alfonso XII of Spain, who is said to have received an opal ring from a vengeful ex lover. He presented the ring to his Queen and soon after that she died under mysterious circumstances.

      Thereafter, whoever in the Royal family wore the ring met the same untimely end. The last victim of the opal ring was the King himself who died soon after he took to wearing it. It didn't occur to the gullible people of the time that the cholera epidemic that was raging through the land might have something to do with the Royal deaths.  
   
       It didn't help opal's refutation at all either when Sir Walter Scott associated the gem with an unfortunate heroine in his novel "Ann of Geierstein". In the book, the heroine Ann is accused of being a demon and she dies after her opal loses all its colour when sprinkled with holy water. Fortunately for the gem, its popularity was soon resurrected by Queen Victoria who absolutely loved the stone and not only wore it herself but also made a point of giving opal jewellery to relatives as wedding presents.
  
 
 
   (5) Crystal Opal                ( 6) White Rough Opal            (7) Pling the Elder,4 writing his book on Natural history in 55 A.D.                                                                                          described opal as the combination of the best characteristics of                                                                                          the most beautiful gems.  
 

      It also helped when a remarkable find of black opals in an area called Lightning Ridge in New South Wales, Australia, helped to revive the market for the gem. Till today, Lightning Ridge remains the source of the world's finest black opals.

      Enough about its history though. Let us first focus on the magical beauty that is opal and how the stone creates the kaleidoscope of colour that has fascinated collectors around the world through the ages. Opal is actually a mineraloid rather than a mineral, meaning that its structure is not crystalline, rather it is amorphous. Opal is a variety of silicon dioxide that contains varying amounts of water. Its chemical composition makes it a relative of its crystalline cousins, the quartz family, however their physical make up couldn't be more different. The amount of water contained in opal varies from specimen to specimen and is typically between 5 - 10% but it can also be a greater percentage of the stone's weight.

  
 
 
 

      Although opal does not really have a crystal structure (meaning a definite regular arrangement of atoms), it does possess a structure of some sorts nevertheless. It is composed of random chains of silicon and oxygen packed into extraordinarily minuscule spheres. These spheres tend to be irregular in size and inconsistent in concentration, but in the precious variety of opal, there are some organised pockets of these spheres. These pockets contain spheres of the same size and have a regular concentration or structure and therefore pockets of differing size and concentration tend to diffract light at different wavelengths creating the play of colours that make this gem so unique.

  
 
     This physical arrangement of spheres only came to light in the 1960s when scientists studied opals using electron microscopes. Like most gems, opals formed millions of years ago. When the deserts of Australia were a great inland sea, there were silica laden sediments deposited on the shoreline. Over time, the sea receded and became what we know today as the great Artesian Basin and released a lot of the silica through the process of weathering, into a solution that filled cracks in the rocks, layers in clay and even morphed into some fossils. This is another unique feature of opal, unlike most gems, it is not igneous but rather sedimentary in origin. The water contained in opal is remnants of the ancient now dry sea. Other areas where opals are found are likely to be in the vicinity of where geothermal springs once flowed. The minerals bubbled up from the beneath the earth's surface and over the course of millennia, lined the cracks, vents and underground cavities in the bedrock. Opal is generally found in areas where the geothermal springs flowed sporadically during seasonal periods of rainfall and then dried up during the dry spells, allowing the minerals to percolate through to the bedrock
 
       (10) Coober Pedy opal field 11) Fossilised shell opal
    (12) PinfireOpal
 
 
      As is evident, Australia is the prime source of opals, and indeed almost 95% of modern opals tend to come from Australian mines. The rest come from Mexico, Brazil, the USA, Ethiopia, Mali, Czechoslovakia, and Hungary but these are not significant additions to the world's opal supply.

      Not all opal is precious though. Common opal lacks opalescence, which is the term used to describe the multicoloured flashes of light that the gem emits. Opals come in many different colours, though white, colourless, pale yellow, pale red, grey, or blacks are common. Its lustre ranges from vitreous to pearly and specimens tend to be transparent to translucent. As it is not a crystalline gem, cleavage is absent and its fracture is conchoidal and the stone tends to be very brittle. The presence of silica gives it its specific gravity of 2 -2.5. It has a very poor hardness, which at 5.5 - 6 on the Moh's scale hardly makes it a durable gem.

      In fact, for all its beauty, it possibly has the worst gemstone characteristics, which if it weren't for the splendour of its opalescence, would render it most unsuitable as a gem. Apart from its softness, its water content, which is responsible for its beauty, is also the cause of its worst features, namely its propensity to dehydration, cracking and sensitivity to heat.

      Opals tend to be prey to a condition called crazing, causing internal cracks in the body of the stone. What makes this an interesting albeit unwelcome phenomenon is that it lacks consistency and is entirely unpredictable. Although it strikes at random, it generally occurs when an opal is removed from damp conditions and is allowed to dry too quickly or if it is exposed to sudden intense light or a combination of these two factors. Crazing can also occur if the opal is subjected to bration, for example during lilting and polishing. A very adual drying process of months and sometimes years is necessary to abilise stones and allow it to be polished witn a substantially reduced risk of crazing, however even this is no guarantee that it will not occur. That is how unpredictable this phenomenon is.

 
 
 
   (13) Bottles carved from boulder opal
 (14) Fish carved in matrix opal                		  
 


      Due to the high water content f the stone, uncut opals are ometimes stored in water to reduce lances of crazing but once the ones are taken out of the liquid, leir susceptibility to crazing actually ncreases. In fact, when opal is mined environment effectively changes nd this alone is enough to induce racks in a small percentage of the ems as soon as a few days after they were mined. In extreme cases of crazing, the fine cracks will intersect and eventually the stone will just crumble.

     Opals are exceptionally sensitive to chemicals and detergents and should never be subjected to sudden changes in light or temperature. At most, a mild soapy lukewarm water solution and a very soft brush are all that should be used to clean jewellery set with opals. Steam cleaning and ultrasonics are to be avoided at all costs. Common sense also dictates that this really is not the kind of gem that one should wear while doing any physical work, especially not gardening or washing dishes, etc. Opals being soft are also extremely vulnerable to knocks and blows and need to be treated as gently as delicate glass or china in their handling. However, opals need to be worn often as the humidity from the air and the skin of the wearer will actually do it good.

     There are literally hundreds of names for opal varieties, some of which are universally accepted and others that are universally ignored or forgotten. Broadly speaking though, there are fundamentally three kinds of opals: precious opal, which is the kind that displays the flashes of fire; the yellow-red fire opal, which is named for its colour as it does not have the flashes of fire; and common opal, which is sometimes also called potch. Common opal is opal that does not display any flashes of colour, although some varieties of common opal may exhibit schillers.


  
 
 
 (17) Wood Opal                   (18) Boulder Opal    (19) Yellow Opal Coins           (21) Precious Fire Opal
 (20) Harlequin Opal                 (22) .............................
 
 

     Precious opal is the variety that has all of the dramatic kaleidoscopic colour play and flashes of fire. This variety is usually classified by its background colour, the particular colour and intensity of colour display and its size. Stones that are predominantly white or light blue are the most common, while those that contain the reds, oranges and violets are more important. Blue and green are more common in precious opal.

     Black opal is a variety of precious opal that is defined by its dark background colour that typically ranges from dark grey to blue-black. Black opals are considered the finest and rarest type of opal. The inclusion of red and orange colour flashes renders the stone even more expensive and its price can match that of fine precious stones. The best black opals come from Lightning Ridge and they are not found anywhere outside Australia.

     White opal on the other hand is precious opal with a light body colour such as white, yellow, cream, etc. It does have the flashes of colour though these are more pastel rather than vivid.

 
 
 
 


    Crystal opal is a transparent to translucent precious opal in which the play of colour is visible on the surface as well as in the interior of the stone. Then there is an interesting variety called Contra Luz opal, which is a variety of precious opal, in which the play of colour is visible one when a light source is behind the stone. It appears to be clear if viewed from the same side as the light source. For this reason, it is more of a collector's gem than that of regular jewellery lovers as its beauty can never be apparent set in jewellery. Another variety, called hydropane, loses its water to become opaque, but can regain its water and become transparent with colour flash once more. Its highly erratic temperament and unpredictability doom it to be a collector's item as well as it really is not suitable for setting in jewellery.

    Then there are flame opals and flash or flashfire opals, neither of which should be confused with fire opals. Flame opal is precious opal whose play of colour consists of red streaks or bands that flicker like a flame when the stone is rotated. Flash or flashfire opal, on the other hand, is precious opal with large schillers that abruptly appear and disappear when the stone is rotated.

  
 

 
 

    Then there is the fabulous harlequin opal in which the play of colour is in a consistent harlequin, diamond shaped or rectangular shaped pattern that is very vivid. Harlequin opal, like black opal, is one of the rarest and most prized varieties of opal. Pinpoint or pinfire opal on the other hand is precious opal with very small pinhead sized flashes of colour. Naturally, this is neither as rare nor as coveted as the harlequin or black opal varieties. Bandfire opal, as its name indicates, displays its colour in wavy bands. Pyrophane is a variety of precious opal in which the play of colour wanders at will and reappears at random in the stone, while rainbow opal but naturally refers to stones that display colour in curved bands like a rainbow.

    Boulder opals are precious opals from Queensland, Australia, that are found in the cracks or as coatings on ironstone and sandstone boulders. Then there is seam opal, which is found in the seams or large cracks of rock. This term may also refer to masses of white common opal containing bands of precious white opal. The difference between the two kinds of opal is that common opal does not exhibit colour play while the display of colour flashes is necessary to qualify it as precious opal. Wash opal refers to waterworn opal pebbles found in alluvial deposits. Yowah nuts are small rounded forms of boulder opal from the Yowah district of Queensland, Australia. They are found in nodule embedded in ironstone. It occurs mostly as walnut sized ironstone nodules containing pockets, veins or sprinklings of precious opal. Opal matrix is thin layers of precious opals on a host rock. They are used in fragments in jewellery.

 
 
 
 

 
    Fire opal is an opal with a yellow, orange or red colour. It does not have any flashes of colour and if it does then it is known as precious fire opal. Most fire opal comes from Mexico, though some amounts of the gem are also found in other locations like the Honduras, Guatemala, USA, Canada, Turkey and Australia. However, most of these occurrences are without much economic value. There are some viable deposits in Brazil though. The colour in fire opal is caused by trace amounts of iron oxide.

    There are also some fascinating varieties of opals that form when opal percolates into the ground and partially replaces wood, bone or shells and thus fossilises them. This variety is called pseudomorphous opal and is further classified as wood opal, bone opal or shell opal. Also fascinating is tabasheer, an opal that occurs as an organic by product. It forms by the hardening of a secretion issued from a certain species of bamboo, forming a porous, rounded mass of opal. Tabasheer is sometimes called vegetable opal. It consists mainly of silica and is used in Oriental medicine.
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    Synthetic opals are also available. Gilson opals, created by Pierre Gilson Sr. in 1974, mimic all the chemical and physical properties of genuine opals. These opals have all the elements of natural opals except water, which makes them beautiful and durable. Gilson opal can be identified by a diagnostic lizard skin effect that can be seen through a jeweller's loupe. Slocum stones are imitation opals made of glass, while opalite is made of plastic.

  
 
 
 


    Opals are generally cut and polished as round or oval cabochons. This is a gemstone that is clearly not suited to faceting and only the best qualities of fire opal can be considered suitable for faceting. Opals are usually found as flat lenses, or thin layers and big pieces are rare. Most of the opals used in commercial jewellery are doublets or triplets. Doublets are combinations consisting of a surface of millimetre thin opal plates, which are mounted on onyx, obsidian, artificial black glass, or common opal. Triplets take this process a step further and sandwich the opal layer between the backing material and a cover made of rock crystal, plastic, hard glass or lead glass for protection.

     When evaluating opal, the thickness of the opal layer is taken into consideration along with the variety, beauty, play of colour, the pattern of the colour display, the cut, the weight and of course, the finish of the stone. With the multitude of varieties, each one of them possessing its own particular attraction, it is sometimes a matter of mood and taste as to which one the wearer prefers. Even the same stone seems new each time you look at it thanks to its lively colour play. While connoisseurs and experts may pontificate on which is the most beautiful variety, it is each person's emotions that decides for him or her which is the most aesthetically pleasing gem. When it comes to choosing an opal, beauty truly does lie in the eyes of the beholder.