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 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 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 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 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 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. 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, 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. 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!

Introduction There are many different types of opal that can be found all around the world, but the most common distinction can be made between common opal and precious opal What makes common opal different from precious opal? Both common opal and precious opal are extremely similar in chemical make-up, being composed of hydrated silica. The differences start in the arrangement of the silica. Common opal In the case of common opal (often referred to by miners and cutters as "potch"), the molecules come together in a disorganised fashion, and this means that light is reflected in the same manner as any normal surface such as a table or chair. No one looks at wonderment at a table surface- because the colours are typically very plain. Precious opal For precious opal, the organisation of materials is very different. Given the correct environmental conditions and sufficient time, the silica precipitates in spheres. Given more good luck, the spheres settle in bands according to size. If this settling process happens just right, the spheres reflect light in the same way a CD, a puddle of oil on water or the feathers on the neck of a male pigeon reflect light. The effect is magical, as if there is colour deep within the opal (or pigeon- but there is not that big a market for cut pigeon). This effect is known as "play of colour". Extracting marketable colours Not all colours are equal. As a general rule, blues are the most common of the colours. The rarity of the colour increases across the spectrum until you get to red which is the rarest of the colours. Very often, the reds are only found in very small patches with lots of inclusions that either make cutting the opal difficult or degrade the material to a point where cutting a gem opal is not possible at all. The colour is usually in a band that is only millimetres deep, and there will almost always be a crack, some sand or something else in there that needs to be removed, while at the same time creating an attractive dome. Cut too deep and the colour disappears, not deep enough and inclusions substantially reduce the value of the stone. When acquiring rough from suppliers I very often get stones in which a cutter has made a mistake and hotly thrown the unfinished opal into an outgoing package. I call these "Hospital rubs". Material required for quality opals Of all the material an opal cutter will buy, only about 10% of it can be successfully converted into an opal, and of these, only 1% will be opals of any substantial worth. This is the major reason why opal in gem form is so expensive. References: Gaillou, Eloise- 2015/04/18, An overview on Gem opals: from the geology to the color to the microstructure

Introduction Of all the gems available for sale, opal is by far the most difficult to understand. This is because of the large variety of opals available, which can look extremely different. Figuring out, therefore what exactly opal is, can be baffling especially to someone who is just looking for a pretty rock to impress their partner. Definitions The classification of opal is made more difficult in the fact it is not even a mineral! It is officially known as a mineraloid, being described as a hydrated amorphous form of silica. Amorphous meaning undefined shape, hydrated meaning having water included in its chemical structure and silica being a mineral composed of silicon. Thanks a lot official definition for not really saying anything! What we can say is that opal is typically some silica (the substance that makes rock rocky) which has been deposited in gaps in rocks. If a crack opens up, some opal may possibly accumulate there. What do you mean by deposition? If you can think back to your high school science class, maybe you were given the task of growing salt or sugar crystals. If you don't remember, or have never done the experiment, basically all you do is dissolve some sugar or salt into some water, heat the water, dissolve more sugar or salt in, until you cannot dissolve any more. Then dangle a string in the solution and let it cool. By doing this, you can grow a big sugar or salt crystal! What works with salt and sugar also works with silica. The major issue however is... have you ever tried to dissolve a teaspoon full of sand into a glass of water? This process takes a very long time. Millions of years in fact. Anecdotally, it seems that if the sand dissolves at all, it doesn't move far from the spot it dissolved before it precipitates out again. This is important for opal cutters because the rough (uncut opal) that they get typically has a lot of sand attached. Anyway. The dissolving and depositing of silica from stuff like sand is how opal tends to appear in rock cracks. There are many different types of opal, but this is a topic for a different discussion.

Opal value is tricky most of the time, but fortunately colour is pretty straightforward. It may surprise you to know that there is a lot of opal around, but almost none of it is valuable, and is therefore never mined and brought to the market. The low value opal has no play of colour, which is the shiny colours that opal is well known for. It may surprise you to know that opal with no play of colour is almost identical chemically to opal with play of colour. Almost. Opals get their colour from a unique arrangement of tiny little spheres that science goes here- if you are interested, I'll post and link an article. The way the particles occur means that reds in opal are the most rare and blues are the most common (relatively). This obviously has an effect on value. The typical progression of colour from most valuable to least is therefore: $$$$$ Red $$$ Yellow $$ Green $ Blue There are some exceptions, but this principal mostly holds true.