Opal Key Facts
- 5.5-6.5 on the Mohs scale of hardness
- October's birthstone
- All opals shine and sparkle in a continually changing play of colours
- The source of opal's sparkle not discovered until 1960
- Mined predominantly in Australia
- Said to help with depression and in the search for true love
General Information on Opal
The name opal was derived from Sansknt 'upala' meaning 'valuable stone'. This was probably the root for the Greek term 'opallios', which translates as 'colour change'. In the days of Roman antiquity there existed a so-called 'opalus', or a 'stone from several elements'.
The Hindu legend tells of a woman desired by three gods at the same time, and who the Eternal changed into a magic cloud. In order to recognize her, Brahma endowed her with the colour of the azure, Shiva tainted her with fiery red, and Vishnu gave her the splendour of the sun; then the Eternal gave her consistence again in the shape of an opal. Another legend says that the opal is born from the sacrifice of a young woman who hurled herself in the funerary pyre of her lover instead of the legitimate wife, whose death was demanded by Hindu rites.
In Europe it was believed that the opal could make one invisible, hence its Middle-ages name of patronus furum (patron of thieves).
In France a specifically French superstition has it that the opal is a jinx. The origin of this belief is the fragility of the opal: lapidaries and jewellers were penalized if they damaged the stones they had to mount, and the frequent breaking of this mineral came to make them feel that it had bad luck attached to it.
Aboriginal legend has it that the creator came down to Earth on a rainbow, in order to bring the message of peace to all the humans. And at the very spot, where his foot touched the ground, the stones became alive and started sparkling in all the colours of the rainbow. That was the birth of the Opals.
Opal is the modern October birthstone and the accepted gem for the 13th wedding anniversary.
For ages people have been believing in the healing power of opal. It is reported to be able to solve depressions and to help its wearer find the true and real love. Opals are supposed to further enhance the positive characteristics for people born under the zodiac sign of Cancer. Black opal is recommended to those born under Scorpio, and boulder opal is the lucky stone for Aries.
Most opal is 50-65 million years old, dating back to the Cretaceous period. Opal formed as silica from decomposing rocks mixed with ground water which formed a silica gel that collected and hardened in underground cavities and fissures.
Opal is a paradoxical gemstone. It is a form of quartz but because opal is actually a gel it is strictly speaking, not a form of quartz. Quartz is a crystalline form of silicon dioxide, opal is a solid gel. However the chemical formula is the same, except that opal is hydrous. i.e. it contains some water which is chemically attached to the silicon dioxide molecules.
The hardness of opal is 5.5 to 6.5 so thought must be given to its durability if you are considering an opal engagement ring.
Opals share one characteristic: they shine and sparkle in a continually changing play of colours, which experts describe as 'opalising'. Depending on the kind, place of occurrence, and colour of the main body, we differentiate dark or black opal, white or light opal, milk or crystal opal, boulder opal, opal Matrix, Yowah Nuts from Queensland and also Mexican and fire opal. Opal variations are practically unlimited. They all show in their own special way the unique play of colours - except for fire opal, which is due to its transparency. If opals are lacking the typical play of colours, they are simply named 'Common Opal'. Precious opal shows a variable interplay of internal colours and does have an internal structure. At the micro scale precious opal is composed of hexagonal or cubic closely packed silica spheres.
Opal's colour play emanates a very special attraction and fascination, but what causes this phenomenon? This question was impossible to answer for a very long time. Only when in the 1960s a team of Australian scientists analysed opals with an electron microscope, it was discovered that small spheres from silica gel caused interference and refraction manifestations, which are responsible for the fantastic play of colours. The spheres, which are arranged in more or less compact structures, succeed in dissecting the light on its passage through the gemstone.
Australia is the classical opal country and today is the worldwide most important supplier of Fine Opals. Almost 95% of all opals come from Australian mines. The remaining five per cent are mined in Mexico, and in Brazil's north, also in the US states of Idaho and Nevada, but recently the stones have also been found in Ethiopia and in the West African country of Mali.
In order to best bring out the play of colour in 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 opal, however, are suited to faceting. The opal cutter will first of all carefully remove any impurities using a diamond cutting wheel, before working out the rough basic shape. Then comes the fine cutting, the finishing with sandpaper and then the final polishing with a wet leather wheel.
Due to the differing percentage of water, opals may easily become brittle. They always contain water - usually between 2 and 6 %, but sometimes even more. Thus if stored too dry or exposed to heat over a longer period of time, opals will show fissures and the play of colour will become paler. Therefore, opal jewellery should be worn as often as possible, for then the gemstone will receive the needed humidity from the air and from the skin of its wearer.
Opals are not very hard: they only achieve 5.5 to 6 on the Mohs scale. Therefore they appreciate a protective setting. In earlier days opal's sensitive surface was often oiled, but today also sealing them with colourless artificial resin has become quite popular.
The value of opal is not only determined by the body colour, transparency and factors based on place of occurrence. (Body colour refers to the basic colour of the gemstone, which can be black, dark or light and coloured). It is also important if the stone is transparent, translucent or opaque. And the opalizing effect may also influence the transparency. The most important criterion for determining the price of an opal, however, is the play of colour, the colours as such and their pattern. If the colour red appears when looking through the stone, all the other colours will appear also. When evaluating opals the thickness of the opal layer is considered, the beauty of the patterning, the cut, weight and finish. Finally the total impression will be decisive.
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Opal is a kind of hydrated silica gel which comes in two varieties. This article gives you all the information you need when choosing an opal.
Part one on the beautiful gemstone that are opals and how their internal structure makes all the amazing colours we see. Also looking at how the you cut, clean and polish opals.