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Of all the gemstones out there, opal is one of the hardest to assign value. The reasons are obvious, diverse and sometimes subtle. This makes almost every aspect of opal, be it mining, purchasing rough, buying that perfect stone for your significant other or investing for future profit quite a challenge. There are however, a few basic ideas that can assist you in getting a rough estimate of a stones value. Cost of rough and market fluctuation From a cutters perspective, opal has to make a profit. A good cutter is capable of spotting and snaring bargains as they occur, but sometimes conditions dictate the price. At the time of writing (16/06/2022) I have watched the price over the last 2 months fluctuate by over 1000 dollars per 100 carats! Generally speaking, prices are dictated by the market, but you will find that sellers will be more reluctant to sell below cost at certain times. Considering the amount of time required to cut a gem I anticipate that some stones in the next few months will be a few hundred over the usual price. I am not immune to all of this, but this cycle I was able to avoid the more outrageous prices- so my stones are relatively unaffected. This is not a future guarantee however. The good news is that recently the price of rough has dipped well below the average price. I think that a lot of buyers have exhausted their funds to keep up their supplies. Precious or common opal? The most obvious place to start is whether the opal is valuable at all. I have written in previous posts that opal can appear in two basic forms, common opal (potch) or precious opal. The differences are pretty obvious, precious opal has play of colour, ie it shines and shimmies. Precious opal goes anywhere from 10 dollars a carat to 10,000 dollars a carat. Potch is pretty much free (although I sometimes buy it online for doublets). Colour of the opal? For those who live in the USA, Australians tend to use the UK spelling for most things. Therefore what you would call "color" is "colour" to us :) Grading system Much effort has been put into a grading system for opal. This is based loosely on the darkness of the colour of the potch backing (body tone or N value), play of colour, brightness of the precious opal, dimensions and of course the weight in carats. Body tone (N value) Body tone chart (taken from opals down under) demonstrating how N values of the potch assist in the classification of a black opal, a dark opal or a light opal. FYI many cutters don't bother differentiating between dark and light if the rough is from Lightning Ridge Body tone impacts the price of opal in a big way. there are only 2 locations in the world that supply black opal on a regular basis, and one of those locations is dubious! Getting a good black opal is therefore very rare, and this obviously affects market availability and consumer demand. As a very rough guide, lets say that a dark opal gets maybe 50 dollars a carat added to the price and a black opal gets 100 dollars. We will do a practical example at the end of this article in which we add up all the values to get a theoretical stone price. Play of colour The part of an opal that everyone wants to see is the shimmer and shine. There are several parts to this, Brightness, pattern and colour. First we will look at brightness: Brightness A typical opal brightness chart- taken from galaxy of opal The measure of an opals brightness is self explanatory. Its how bright the colours are. There is a lot of science behind this and I will cover this in excruciating detail, but basically shiny=good. The scale goes from B7 (can barely see the pattern) to B1 (so bright it nearly needs a warning label). A rough rule of thumb says that each unit of brightness is worth 50 dollars a carat. So a B7 is 50 bucks a carat, a B1 is 400 dollars a carat. Please don't take these numbers as binding, they are only the roughest of guides. So far, an opal that is black with the brightest colours is about 500 bucks for a 1 carat stone. Lets put the other modifiers on and see what happens: Pattern Opal patterns are ridiculously hard to quantify. This is because an opal is essentially an individual. their pattern can be considered to be a fingerprint. Nevertheless, after studying a few opals, one can see that they fall into a few pattern categories, no doubt determined by the conditions of formation. Some brave souls have attempted to classify these patterns. We therefore have a few industry accepted opal patterns that have a range of values. I'll just zoom in on a few to give you an idea. Moss pattern An image from opal auctions of a moss pattern gem This pattern can be considered a standard type of pattern. Best described as a pattern that looks like shiny moss growing on the stone. If an opal has this pattern, it is most likely that its value will be derived from other attributes such as brightness and body tone, but it can be quite an attractive opal. I would suggest there would be not much of an increase in price for this pattern Chaff pattern An image of a n opal with chaff pattern. Source: Opal auctions An opal with a chaff pattern can be considered to be quite special. Chaff can be described as a series of small lines that pervade through the stone. Very often, an opal cutter will mention that chaff pattern is within the stone even if another pattern dominates. You can expect the value of a true chaff stone to increase by at least 150 dollars a carat. Mosaic pattern A mosaic opal pattern thanks to Treasurion.com There are plenty of valuable opal patterns but the most sought after tends to be the mosaic pattern. This pattern can be identified by large, regular shapes of colour flaking all over the stone. One could expect a mosaic pattern stone to fetch an extra 250 dollars a carat. Colour I'll let you work out what a colour is. The value of colour on an opal goes from purple, to blue, to green, to yellow to red. blue may be 20 dollars a carat, green and yellow 50 dollars and red 100 dollars a carat. Weight There are a few tricks to weight: the first is that the measure of an opal (carats) is tiny! about 0.2 grams per carat, or 0.007 ounces in American money. The second is that the price per carat is not linear. a 3 carat stone may well be 10x more expensive than a 1 carat stone. This measure of all the measures I have mentioned is the most flexible but we will give quantifying it a go: I suggest that we call this a geometric sequence of 2... and I am so sorry for the math! So the value of an opal goes up by a double factor for every carat, eg a 2ct stone is 2x1ct stone, a 3ct stone is 4x the 1ct stone, a 4ct stone is 8x the value of a 1ct stone and so on. Are we ready to try this out? A 2ct N1 opal, red with highest brightness and a mosaic pattern should be roughly... 100+400+100+250 x 4 = $3400! Lets see if we can find a stone for that price. Checking Black opal direct: So this formula gives a much lower value to what a top opal cutter would ask. I would suggest however that the prices we charge are more in line with that formula- seeing I use it all the time... And this is only just a guide. I hope it helps! See you next time :)

One of the most fascinating types of opal out there is matrix opal. This is a type of opal which has typically seeped into and fused with more porous rock types. The exact process changes from rock type to rock type and region to region but generally speaking a sedimentary rock either has parts of the glue holding it together (known as matrix) replaced by silica over time, or the tiny pores within the rock itself fill up with silica. The result is the same- the silica is of course opal. Andamooka and its opal Andamooka matrix opal has an interesting history. The town, Andamooka is located in South Australia, near Coober Pedy. It is extremely remote. The town itself has a frontier quality to it. Nevertheless, it is one of the oldest mining towns in Australia. Originally when opal was discovered in this remote part of the world, miners were more interested in the crystal and boulder opal that was extracted. These opal types had obvious colour and was easily sold at a premium price. It didn't take long, however for miners to realise they could treat the "waste" matrix opal using common household chemicals. The town of Andamooka (source aussietowns.com.au) Treating the opal Matrix opal tends to be porous. This is important, as if the opal can soak up water, it can also soak up treatments. The most common treatment methods involve either smoking or a heat treatment using ordinary table sugar. The result is an originally light coloured rock which is now intensely dark, and this dark colour brings out the fire of the opal within. The Andamooka opal con Once miners realised heat treatments changed the colour and vibrancy of the opal, How to Heat Treat Andamooka Matrix Opal,https://www.youtube.com/watch?v=M4VLolDn0DA it didn't take long for some of the less reputable miners to try to pass off this opal to foreigners as original Lightning Ridge opal. In reality, this opal is easy to identify so the "con" should not have been too effective. As they say there is a sucker born every minute.... The reputation plummets As fantastic as it may seem, this "fake" opal was successfully marketed, but it did not take long for the deception to be revealed. In a market reaction not dissimilar to what we see in smoked Ethiopian opal in the present day, All treated opals became practically worthless overnight. There was no market in Andamooka matrix. Opal production dwindled. The recovery Over the last few years, the value of Andamooka opal has been rediscovered. The treatment recipes managed to survive. Most people use a treatment method that is at least 40 years old and is probably unchanged from colonial times. Many opal sellers specialise in "Mooka" (slang for Andamooka opal) and many YouTube influencers demonstrate the treatment technique to millions of adoring viewers. Andamooka is back and although affordable, is becoming more expensive every year. Unbelievable Discovery! The Finest of all Opals - Gem Matrix - (Andamooka Matrix Opal),https://www.youtube.com/watch?v=ohi-5UtWZvI Mining Andamooka mining is still possible but claims have to comply with the requirements of the local indigenous people. For centuries, the local tribes were not considered at all and they have a right to feel aggrieved about the land and what was stolen. Meeting tighter and tighter requirements is drying up supply of this wonderful opal. there may be a time in the near future when it is not available at all. Conclusion Although Andamooka and its opal got off to a rocky (groan) start, This fine gem is making a massive comeback. Look on our site for some Andamooka matrix. I'm sure it won't stay there for long!

All opal is an almost magical gem. The way it glitters in the light has an almost fairy-tale feel when you see a truly gorgeous stone. The amazing nature of the stone combined with the premium prices attracted by top specimens, unfortunately also attracts sellers anxious to make the top dollar without going through the effort of cutting or acquiring top products. How do you, the buyer, decide on where and what to buy? How can you spot the real article as opposed to a fake or lesser type? here is a helpful guide, assisted by respected industry leaders who have graciously allowed me to use some of their materials in order to help you make the most informed decisions on the best quality or value opals. What kinds of opals are there on the market? There are literally hundreds of different opal types on the market. In order to make an informed decision, however, it is possible to narrow down the vast variety of different opal types into two categories which will greatly assist you in assessing the quality of an opal. These two categories are: Treated or untreated and Country of origin Treated vs untreated Opals can be treated in a variety of ways. Basically this treatment can be broken down into colour enhancement and stabilisation. Colour enhancement is using smoking, dyes or chemical treatment to artificially darken the stone, thus enhancing its colour. Stabilisation is using external materials to enhance the strength, size or colour of the stone. The easiest treatment to detect is the doublet or the triplet. These are stones that have a thin section of precious opal glued onto a piece of common opal or rock. Here is a video from Riley Gunn, a well known supplier of opal on the doubleting method: Opal Doublet Making 101,https://www.youtube.com/watch?v=F9X2c-PqQhQ Here is a well known YouTube channel- Roy's Rocks demonstrating how to spot a doublet: Solid Opal VS Opal Doublet VS Opal Triplet. How Do You Tell Them Apart? Real Examples.,https://www.youtube.com/watch?v=9fSn8E5uWes As with most of the things mentioned here, there is nothing inherently wrong with treating a stone, in fact for certain types of stone, treatment is the industry standard. if a stone is treated however, the seller should explicitly state that the product you are buying is a treated stone. This gives the consumer the freedom to make their own choices on the opals they buy. Country of origin All opal is special in its own way, and certain regions are known for certain types of opal. The international trade of opals all around the world is a good thing and should be encouraged. Its only when people are deliberately mislead about the origin of their opals, that issues of country and production emerge. Deceptively marketed opals do damage to both the consumer and the legitimate producers of all opals. If, for example an Ethiopian opal is marketed as Australian, the deception damages the reputation of both countries. Ethiopian opal being a beautiful stone in its own right merely being seen as a fake, and the good properties of quality Australian opals brought into question by mis-marketed stones that don't add up to expectations. Ethiopian opal The most commonly substituted opal is Ethiopian opal. The basic reason for this is that a huge deposit of cheap opal has been discovered in Ethiopia. It is therefore very tempting for agencies to market this cheaper opal as Australian, Mexican or other varieties. The basic test for Ethiopian opal is to wet the stone. As this kind of opal is Hydrophane, It will typically soak up moisture and go clear. Photography: we all to a certain extent put some effort into the presentation of our opals, but not to the extent that the opal is misrepresented. There are many hacks that can be applied to images to make opals appear better than in real life. Rather than presenting a few paragraphs on the topic, I'll let an expert, Riley Gunn explain it on his video: Have You Seen This Opal?,https://www.youtube.com/watch?v=DGZ3IMScys0 Conclusion: It is my hope that people can trust online sellers to do the right thing and sell, more or less what they say they are selling. These few tips should help the new opal buyer to navigate some of the hazards should a merchant be less ethical. Have a nice day!