Opal Web Site : CLASSIFICATION REPORTS .
Classification reports for the following types of opal should include these details:
Natural Opal .
- Type of opal .
- Variety of opal as Black opal, Dark opal or Light opal with a body classification from N1 (Black) to N9 (White) based on the AGIA Body Tone Chart.
- Transparency as opaque, translucent or transparent. Note if it is crystal opal.
- Weight and dimensions .
Treated Opal .
1. Type of opal.
Variety of opal as Black, Dark or Light opal .
Transparency as opaque, translucent or transparent. Note if it is crystal opal.
Type of Treatment and process if known .
Weight and dimensionsComposite Opal .
- Type of composite as doublet, triplet, mosaic or chip opal .
- Treatment process, where relevant .
- Dimensions .
Synthetic and Imitation .
Gemmological category including manufacturer (if known) .
Description (Body Tone) .
If composite, mention type as doublet, triplet, mosaic or chip .
Weight and dimensions, only dimensions if compositeOrigin .Any indication of the origin of opal by the use of geographical location should not be used unless it is qualified as an indication of the type of locality only as recommended by the International Confederation of Jewellery, Silverware, Diamonds, Pearls and Stones (CIBJO) such as Lightning Ridge type black opal.AUSTRALIAN OPAL AND GEM INDUSTRY ASSOCIATION LIMITED.
A.C.N. 001 117 237.
Suite 309, Grand United Building, 149 Castlereagh Street, Sydney 2000, Australia.
Precious opal has been known from ancient times. It is a valuable raw material for use in jewellery. On the world market, the price of the precious opal continuously increases with time. The old European opal mines are now depleted, and the main supplier of the precious opal to world markets is Australia.
How Opal Colour is Produced.
Chemical formula Si02.nH20 and the name deriving from the Ancient word ”opalus”, meaning to see a play of colours, opal’s unique precious gemstone consists of Hydrated amorphous Silica. The unique ‘play of colours’, characteristics of Opal, are caused by a myriad of minute silica spheres cemented together by silica gel.RI: 1.450
Birefringence: None.
Optic Character: Single Refractive.
Specific Gravity: 2.15.
Hardness: 6 average.
Transparency: Opaque to TP.
Special Identifying Properties and Tests: Play of color, low refractive index, SG, magnification should be diagnostic.
Synthetics: Gilson synthetic is easily identified by its snake skinappearance. I have slides of this material that I will be adding. Glass imitations are easily identified by their coloration and varying RI.
Imitations: Many.
Australian opals are found in irregular nodules or “nobbies” or in steams, the ‘Australian Black ‘Opal gets its name from the background colour which maybe a dark grey known as a semi-black to an intense black background which is the most desirable. Visual colours or ‘face up display’ which is term to indicate colour directly to the viewer, range through blue, green, orange and red. The finest and rarest of gems occurs when ”red on black” combines to show a full array of spectral colours.
Opal Web Site : Mystery.
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. The fantastic colour play of Opal reflects changing emotions and moods of people. Fire and water, the sparkling images of Boulder Opal, the vivid light flashes of Black Opal or the soft shine of Milk Opal – striking contrasts characterise the colourful world of this fascinating gemstone. Maybe this is the reason why it depends on our daily mood which Opal we prefer. Opals are like human emotions: you always experience them different and anew.Opal web site : Care of Opals and Opal JewelleryOpal jewellery requires no greater care than other jewellery mounted with stones such as diamond, ruby emerald, tanzanite or turquoise.
You should never wear any jewellery in rough conditions such as to the beach or during activities where it may get knocked by metal or hard objects (eg washing up).
In these conditions, stones get dislodged from their settings, gold gets scratched and stones get chipped (even diamonds) and opal should be treated the same as all other stones – with respect.
Opal requires no special treatment or care. As with other stones, grime from wear can be wiped off with a damp tissue or cloth.
Opal is a form of silica, chemically similar to quartz, but containing water within the mineral structure. Precious opal consists of small silica spheres, of uniform size and arranged in a regular pattern.The colour in precious opal is caused by the regular array of silica spheres diffracting white light and breaking it up into the colours of the spectrum. The play of colour in opal depends on the angle of incidence of the light and can change or disappear when the gem is rotated. The size and spacing of the spheres also controls the colour range of opal. In opals showing reds flashes, the spheres are larger than those showing only violet or green flashes.In potch opal and common opal the silica spheres may be absent or too small or irregularly arranged to produce colour.
It took the development of the electron microscope to work this out. Precious opal is made up of tiny uniform spheres of transparent hard silica, which fit together in an orderly three dimensional frame, sitting in a “bath” of silica solution. It is the orderliness of the spheres that separates precious opal from common opal.
Light passes through the transparent spheres in a direct line, but when it hits the ‘bath’ of silica, it is bent and deflected at different angles, thus producing a rainbow effect.
October birthstones — OPAL The name opal is derived from the Sanskrit word “upala,” as well as the Latin “opalus,” meaning “precious stone.” Opal is a gemstone of much variety.
Hydrated silica material, made of submicroscopic silica spheres held together by more silica and water. It is a soft stone, easily altered in appearance by changes in heat and pressure. This mineral contains varying amounts of water within it that determine the appearance of the gemstone. When water evaporates out of an opal, the stone appears slightly smaller and the stress of the evaporation creates cracks on it.
Volcanic rocks, within cavities and cracks. In sedimentary volcanic ash rock, percolating water in the ground dissolves silica that eventually precipitates to form the opal, sometimes becoming the replacement material for fossils — shells, bones, wood — whose original material had dissolved away.
Opals play of colors many stones flash the colors of the rainbow when moved, due to the interference of light on small cracks and other internal structural differences. Opals also have characteristic colors due to impurities within the stone. The milky or pearly appearance of some opals are due to inclusions of tiny gas bubbles. Yellows and reds betray the presence of iron oxides. The spectacular black opals that sometimes flash green, blue and red get their color from magnesium oxides and organic carbon within the stone. Perhaps the most valuable opal pattern is the “harlequin,” large angular patches of red, yellow and green resembling the checks on a clown’s costume.
Australia noted for its magnificent black opals. Fire opals were first mined in Mexico, and continue to be produced today. In the United States, brilliant fire opals are also found in Nevada. Other commercial sources of opal are Brazil, Honduras, Nicaragua, Guatemala, Japan and Ireland.
To ancient Romans Orientals called it the “anchor of hope.” Arabs say it fell from the heavens in flashes of lightning. It was believed to make its wearer invisible, hence the opal was the talisman of thieves and spies.
During the Medieval period, a change in color intensity of an opal was believed to indicated if its wearer was ill or in good health. The opal was supposed to maintain a strong heart, prevent fainting, protect against infection, and cleanse foul-smelling air. The stone, as in ancient times, was still regarded as a symbol of hope.
But the opal’s reputation changed in the mid-14th century. The Black Death swept across Europe, killing one quarter of its population. The gem was believed to be the cause of death. When worn by someone struck with the deadly plague, it would appear brilliant only until the person died. Then it would change in appearance, losing its luster. In reality, it was the sensitivity of this stone to changes in temperature that altered its appearance, as the heat from a burning fever gave way to the chill of death.
In Elizabethan England, the opal was treasured for its beauty. Shakespeare wrote of it in the Twelfth Night as the “queen of gems.” Queen Victoria presented her children with opal jewelry, thus making the the stone popular.
Opals were probably first mined around 4000 B.C. in Ethiopia, but their popularity did not grow until the Romans embraced them around 100 B.C. By then, the majority of opals were mined in Hungary. For over a 1,000 years Hungary supplied European rulers and churchmen with the treasure of opals. During that time powers good and bad were attributed to opals.In 1829, Sir Walter Scott wrote a novel, Anne of Geierstein. The public misread the story and assumed the opal caused misfortune to come upon the heroine. This reinforced the idea of opals being bad luck, and the opal market dropped in the aftermath. At the same time, Australian opals began appearing in the market, but dealers were hesitant because the Australian opals were much more brilliant and some assumed they were fakes. Queen Victoria fell in love with these gems and her passion helped restore opals as a popular stone. By the turn of the century, Australia had become the world’s primary supplier of opals.
Depending on the size of the spheres, varying colours of the spectrum are diffracted. So it is a combination of deflection (bending) and diffraction (breaking up) of light rays that creates the colour in opal. If you move the stone, light hits the spheres from different angles and bring about a change in colour. The name opal actually means “to see a change in colour.” The way in which colours change within a particular stone as it is rotated and tilted is called the stone’s play of colour.
The size of the spheres has a bearing on the colour produced. Smaller spheres bring out the blues, from one end of the spectrum. Larger spheres produce the reds from the other end. The more uniform the spheres are placed, the more intense, brilliant and defined the colour will be.
When buying diamonds, sapphires or rubies, you have either a real one or a synthetic. But with opal you can buy an expensivesolid stone, or you can buy a triplet or a doublet. Doublets and triplets are far more affordable than solid opals, and they are still real opal.
Black Opal or Opal with a dark grey body shows the most brilliant play of colours imaginable. Crystal opal, which comes immediately after Black Opal in the hit list, should be more transparent with a deep play of colours. White or milky Opals show more diffuse colours and are the least expensive Opals.
Solid Opals. A solid opal, as the name implies, is a single piece of opal. Solids may be cut into a variety of shapes ranging from circular hemispheres and ovals to free-flowing shapes that follow the natural lines of the stone.
Doublet Opals. Doublets are created by taking a thin sliver of natural crystal opal, then attaching it with jewellers cement to a natural black opal backing. (The backing is called black potch and lacks the play of colour charateristic of opal.)
Triplet Opals. A triplet is also a composite piece. To create a triplet, the jeweler takes a sliver of natural crystal opal, then attaches it with jewellers cement to a backing of black potch. A cap of clear quartz is then placed on top of the opal sliver, creating, if you will, a sandwich effect.
Most solid opals and doublets are cut and polished with a convex dome or curved top. This encourages light into the stone so that the opal’s irridescent properties are shown at their best. For triplets, the dome is created by a crystal cap that covers the flat slice of opal.
Rough opal parcels are sorted into three grades: tops, middle, and low. Each tops parcel has a King stone, which is the best stone in the parcel. Some parcels have several King stones. Colour is the primary criteria for grading, but the graders also take into consideration the number of imperfections and faults, and whether a stone is the right shape to be cut into an oval or one of the other popular shapes.
You can buy rough opal in several different conditions.
Mine Run. Direct from the mine. The stones have not been cut or ground down. This means that there is more guess work in the cutting. Purchasing mine run opal can be risky if you are not very experienced.
Off Cuts. The miner has removed whatever opal he has a market for and sells you what’s left. With off cuts, you can usually tell what you are going to be able to cut. You must still watch for cracks in the opal because once a crack becomes obvious, a stone can lose half its value.
Rubs. This can often be the best way of buying rough if you are not very experienced. The miner has cut and ground the stones into basic shapes, after having removed most of the rubbish. What you have left is the stone nearly ready for the dopping and polishing process. You have the satisfaction of cutting your own stones without the high risk of buying mine run rough.
Opal Web Site : Features of Opal that Determine PriceWith each stone it is important to consider :
- Colours present in the stone (also called “play of colour”) .
- Brightness of the stone – called the “fire” .
- Whether the stone is black, dark, boulder or light body tone .
- How saturated or intense the colours are .
- Whether the stone appears dull from any angles .
- Whether the stone is flat on top or has a rounded dome .
- The size and weight of the stone .
- The cut of the stone – even oval, or irregular freeform .
Opal Buying and Pricing Guide Tip 1. Under nearly all circumstances if a certain opal appeals to you that is the one you should buy. Often our intuition is the best judge! Tip 2.When purchasing opal some key words to look for are : A. Triplet a very thin slice of opal enhanced by blackening the underside of the opal to make the colours stronger and a quartz or plastic dome placed on top of the opal to magnify the colour and pattern. The advantage is they are cheap and fit readily into standard size jewelry. B. Doublet a thicker slice of opal with a blackened underside. The advantage over a triplet is the surface is real opal and affords a greater depth of colour. C. Solid as the name suggests a real and solid opal with no add ons. Therefore A has less value than B which has much less value than C when size colour and pattern are the same. Tip 3. Laboratory produced or treated matrix opal have far less value than triplets, doublets and solids. Tip 4. Solid opals come in many variations, if size pattern colour and shape are the same the most valuable opal will be.. 1Black opal the rarest and most highly prized of all. The best black opal comes from Lightning Ridge, Australia. Black opal has very rich and striking colours that are formed on a dark or black potch base. This dark base intensifies the colour. Black opal has been sold for as much as $14,000 per carat wholesale or field price. Outstanding quality for $10,000 per carat field price. Black opal with all the colours and good quality starts at around $2,000 per carat on the field. The opal may go through many sets of hands before arriving in the retail shop and so the retail price is much higher. Top quality black opal is very rare and in relation to many other gemstones is probably under priced. The investment potential for even medium grades of black opal is very very interesting. This is a resource that is fast disappearing ! 2 Boulder opal especially the darker variety. Boulder opal gets its name from the fact that an ironstone backing is part of its natural formation, the colours can also be quite brilliant and dazzling and gem quality also brings a high price almost matching the black opal prices. It would appear that there is a larger production and it is found over a much wider area (mainly Western Queensland ) than black opal and so the price of average grade material is somewhat lower. 3 Crystal opal or fire opal. This variety of opal can also be extra ordinarily beautiful and gem material can sell for $1000 per carat wholesale or field price. This opal is translucent and even transparent when held up to the light. Lightning Ridge, Andamooka and Coober Pedy are all produces of gem materials. Thinner pieces of crystal opal make the best doublets and triplets. 4 White opal. Gets its name from the white potch the colour forms on or in. Coober Pedy has produced very large quantities of white opal. This opal is much cheaper than the above mentioned varieties. This is partly due to some of this material being quite porous and brittle. However some white opal is still very attractive indeed and some of it is quite stable. 5 Water opal. I have left the Mexican water opal last, partly because it generally doesn’t have the fire of the other opal families and partly because I haven’t seen all that much of it. I have never been to the areas where it is produced, nor did I wish to leave this important category out. *Please note there are many opal fields in the world but because 90% of the World’s production comes from Australia I have concentrated on them. Brazil, U.S.A., Honduras and Indonesia also produce opals. Tip 5. Brightness of colour, play of colour ( what the colour does when you move the stone ) general appeal including patterns or pictures and colour combinations are all determining factors when valuing an opal. When these factors are the same then red will be the most valuable, followed by pink orange gold yellow green and the blue and then purple. Part of the reason for this value scale is that purple is the most common and red the rarest. Just to put things in perspective though, an opal showing very bright or electric blue can be valued as highly as an average red opal all other things being equal ! Tip 6. Use your intuitionOPAL NOMENCLATURE AND CLASSIFICATION Australian Gemstones: Opal INTRODUCTION Opal is Australia’s National Gemstone. Australia produces 95% of the world’s natural precious opal supply. This nomenclature encompasses all types and varieties of opal to provide a standardisation of terminology but does not establish any valuation methodology. The Australian Gemstone Industry Council Inc., in collaboration with the Australian Gem Industry Association Ltd., the Gemmological Association of Australia Ltd., the Lightning Ridge Miners Association Ltd. And the Jewellers Association of Australia Ltd., has produced the following nomenclature for the classification of opal. OPAL CLASSIFICATION Opal is a gemstone consisting of hydrated amorphous silica with the chemical formula SiO2.nH2O. There are two basic forms of opal described by visual appearance. Precious Opal – is opal which exhibits the phenomenon known as play-of-colour, produced by the diffraction of white light through a micro-structure of orderly arrayed silica spheres to produce changing spectral hues. Common Opal and Potch – is opal which does not exhibit a play-of-colour. The distinction between common opal and potch is based on formation and structure. Potch is structurally similar to precious opal but has a disorderly arrangement of silica spheres. Common opal shows some degree of micro crystallinity. TYPES OF NATURAL OPAL Natural opal is opal which has not been treated or enhanced in any way other than by cutting and polishing. There are three types of natural opal, with varieties described by the two characteristics of body tone and transparency. Natural Opal Type 1 – is opal presented in one piece in its natural state apart from cutting or polishing and is of substantially homogenous chemical composition. Natural Opal Type 2 – is opal presented in one piece where the opal is naturally attached to the host rock in which it was formed and the host rock is of a different chemical composition. This opal is commonly known as boulder opal. Natural Opal Type 3 – is opal presented in one piece where the opal is intimately diffused as infillings of pores or holes or between grains of the host rock in which it was formed. This opal is commonly known as matrix opal. VARIETIES OF NATURAL OPAL The variety of natural opal is determined by the two characteristics of body tone and transparency. Body Tone The body tone of an opal is different to the play-of-colour displayed in precious opal. There are three varieties of natural opal based on body tone. Body tone refers to the relative darkness or lightness of the opal when ignoring the play-of-colour. Black Opal – is the family of opal which shows a play-of-colour within or on a black body tone by reference to the AGIA Body Tone Chart N1, N2, N3 and N4 when viewed face up. Dark Opal – is the family of opal which shows a play-of-colour within or on a dark body tone by reference to the AGIA Body Tone Chart N5, N6 when viewed face up. Light Opal – is the family of opal which shows a play-of-colour within or on a light body tone by reference to the AGIA Body Tone chart N7, N8 or N9 when viewed face up. The N9 category is referred to as white opal. Opal with a distinct coloured body (such as yellow, orange, red or brown) should be classified as black, dark or light opal by reference to the AGIA Body Tone Chart with a notation stating its colour hue. Transparency Opal shows all forms of diaphaneity and ranges from transparent to opaque. Natural precious opal which is transparent to semi-transparent is known as crystal opal. Crystal opal can have either a black, dark or light body colour tone. The term “crystal” in this context refers to appearance not a crystalline structure. OPAL TREATMENTS Opal can be subjected to various types of treatment. Present CIBJO guidelines state that any method of treatment other than standard cutting and polishing must be disclosed and the process used specified on all invoices, advertising and commercial documents. Types of treatments include colour enhancement, heating, painting, dying, resins and waxes, oiling or any application of chemicals. Opal is treated to change its natural appearance, structure or durability. Opal is colour enhanced in opal inlay jewellery where usually a thin solid crystal opal has black paint or glue applied or set above black painted jewellery. COMPOSITE NATURAL OPAL Composite natural opal consists of natural opal laminates, manually cemented or attached to another material. The opal component is natural opal. There are three main forms of composite opal: Doublet Opals – are a composition of two pieces where a slice of natural opal is cemented to a dark base material. Triplet Opals – are a composition of three pieces where a thin slice of natural opal is cemented to a dark base material and a transparent top layer, usually of quartz or glass. Mosaic and Chip Opals – are a composition of small flat or irregularly shaped pieces of natural opal cemented as a mosaic tile on a dark base material or encompassed in a resin. SYNTHETIC OPAL Synthetic Opal is material which has essentially the same chemical composition and physical structure as natural opal but has been made by laboratory or industrial process. Synthetic composites exist as synthetic doublets, triplets or mosaics and must be disclosed as synthetic composites. IMITATION OPAL Imitation Opal is material which imitates the play-of-colour of natural opal, but does not have the same physical and chemical structure or gemmological constants as natural opal. CLASSIFICATION REPORTS Classification reports for the following types of opal should include these details: Natural Opal 1. Type of opal 2. Variety of opal as Black opal, Dark opal or Light opal with a body classification from N1 (Black) to N9 (White) based on the AGIA Body Tone Chart. 3. Transparency as opaque, translucent or transparent. Note if it is crystal opal. 4. Weight and dimensions Treated Opal 1. Type of opal 2. Variety of opal as Black, Dark or Light opal 3. Transparency as opaque, translucent or transparent. Note if it is crystal opal. 4. Type of Treatment and process if known 5. Weight and dimensions Composite Opal 1. Type of composite as doublet, triplet, mosaic or chip opal 2. Treatment process, where relevant 3. Dimensions Synthetic and Imitation 1. Gemmological category including manufacturer (if known) 2. Description (Body Tone) 3. If composite, mention type as doublet, triplet, mosaic or chip 4. Weight and dimensions, only dimensions if composite Origin Any indication of the origin of opal by the use of geographical location should not be used unless it is qualified as an indication of the type of locality only as recommended by the International Confederation of Jewellery, Silverware, Diamonds, Pearls and Stones (CIBJO) such as Lightning Ridge type black opal. See also: What is an opal? AUSTRALIAN OPAL AND GEM INDUSTRY ASSOCIATION LIMITED A.C.N. 001 117 237 Suite 309, Grand United Building, 149 Castlereagh Street, Sydney 2000, Australia Phone: + 61 2 9267 1310 Fax: + 61 2 9267 1037
Numerous legends and tales surround this colourful gemstone, which can be traced back in its origins to a time long before our memory, to the ancient dream time of the Australian aborigines. It is reported in their legends 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.
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”. In the days of Roman antiquity there existed a so-called “opalus”, or a “stone from several elements”. So the ancient Romans may already have had an inkling why the Opals show such a striking play of colours. But we will come to this later.
Pliny, the famous Roman author, called Opal a gemstone which combines the best possible characteristics of the most beautiful of gemstones: the fine sparkle of Almandine, the shining purple of Amethyst, the golden yellow of Topaz, and the deep blue of Sapphire, “so that all colours shine and sparkle together in a beautiful combination”.
Up to the first half of the 19th century, Opals were relatively rare. But then their career boomed suddenly and made them one of the most popular gemstones, and the start of this development brought them to the gemstone cutters of the gemstone centre of Idar-Oberstein. In the era of Art Deco the Opals experienced their flourishing, with contemporary gemstone artists preferring them to all other stones because of their subdued charm, which in turn was excellently suited to be combined with enamel, another very popular material of those days.
The history of Australian Opal began actually millions of years ago, when parts of Australia were covered by a vast inland sea, and stone sediment was deposited along its shoreline. When the water masses flooded back, they flushed water containing silica into the resulting cavities and niches in the sedimentary rocks, and also the remains of plants and animals were deposited there. Slowly the silica stone transformed into Opal, for basically Opals are simply a combination of silica and water. Or, to be more precise: Opals are a gel from silica, with varying percentages of water.
- Amorphous .
- Shapeless. Not consisting of crystals. Non crystalline. Glass is amorphous. Sugar is crystalline.
- Deflection .
- The bending of rays of light from a straight line.
- Diffraction .
- The Breaking up of a ray of light into either a series of light and dark bands, or into coloured bands of the spectrum.
- Diffuse .
- To spread out so as to cover a larger space or surface. To scatter.
- Fluorescent .
- A light produced by the electrical stimulation of a gas or vapour. Fluorescent lights have a similar effect on opal as a bright cloudy day–they do not properly bring out the colours in opal
- Hydrate .
- A compound produced when certain substances chemically combine with water.
- Incandescent .
- Glowing with heat (red or white hot) as in a light bulb which glows white hot, but produces a light that more closely simulates natural sunlight. Sunlight and incandescent lights bring out the natural colours in opal.
- Opal .
- Opal comes from the Latin word opalus which means to see a change in colour. Chemically, opal is hydrated silica, similar to quartz.
- Opalescence .
- A play of colour, similar to that of an opal.
- Opaque .
- Not allowing light to pass through. The opposite of transparent.
- Play of Colour .
- The way in which colours change as an opal is tilted in different directions.
- Silica .
- (Silicon Dioxide) A hard, white or colourless substance, that in the form of quartz, enters into the composition of many rocks and is contained in sponges and certain plants. The needle in the mouth of a female mosquito is made of silica. Flint, sand, chalcedony, and opal are examples of silica in different forms.
- Spectrum .
- The band of colours formed when a beam of white light passes through a prism or by some other means (e.g. mist or spray, in the case of a rainbow) The full range of spectrum colours are: red, orange, yellow, green blue, indigo, and violet.
- Sphere .
- A round three dimensional geometric shape whose surface is equally distant at all points from the centre point.
- Translucent .
- Letting light through without being transparent.
- Transparent .
- Easily seen through.(glass like) .
Opal uncut opal on the internet, buy samples first if possible. If some of the rough is faced it makes the opal rough parcel far less risk. If you’re buying opal on the opal fields try to find clues in the rough parcel. Most rough is sold wet so you can see the colors as they will be when they are polished. This is standard practice. However it pays to wipe a few bits dry as this will show up any crazing or cracks often caused from contact with jackhammers or bulldozers etc ! Faced pieces will show up the general character of the whole parcel usually. Opal miners don’t mind you taking a good close look at their product, but if you find something you don’t like be discreet. Never knock or rubbish some ones opal….. They’ve probably worked really hard for it and they won’t like unkind comments and you won’t like being hung upside down by one leg over a deep mineshaft either!
Boulder opal gets its name from the fact that an ironstone backing is part of its natural formation, the colours can also be quite brilliant and dazzling and gem quality boulder opals also brings a high price almost matching the black opal prices. It would appear that there is a larger production and it is found over a much wider area (mainly Western Queensland ) than black opal and so the price of average grade material is somewhat lower.There is also boulder matrix opal which has tiny lines of colour running through the boulder host rock. This material is cheaper but attractive and popular in Germany as a semi-precious form of opal.
OPAL WEB SITE
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eflection & Diffraction.
