Opals, Australia’s national gemstone. The term ‘opal’ comes from the Roman term ‘Opalus’ meaning ‘precious jewel’. They have been called the “Queen of gems” by Shakespeare and the tears of Zeus by the ancient Greeks. Opals are unique in displaying a multitude of colours whilst most gemstones only present one or two at most.
Australian opals are widely considered to be the highest quality produced around the world. Australia has also been, traditionally, the largest producer of gem quality opals. Up until recent years, Australia provided over 90% of the world’s supply.
At this stage I want to add that GoldOz has no financial interest in opals or the Australian opal industry. We just love opals! We also love helping out our Australian miners.
What are Opals? Click here to learn about what makes an opal.
Value
The Quality of Australian Opals
Australian opals are generally recognised as of the highest quality produced anywhere in the world. We also have some of the rarest. For instance, the extremely rare black opal sub-classification have only ever been found in Australia.
Opal quality, and therefore value, is measured differently than for other gemstones. For opals, the brilliance of the colours (enhanced by their base colour) and which colours are present have a large impact on the value of the stone.
Brilliance is easily understood. The brighter the colours the better. However, which colours are present also matters. Not all colours are worth the same either. Red is the most valuable colour and is also the rarest. Orange is also rare and the next most valuable. This continues on to yellow, then green and finally blue which is the most common colour.
Australian opal is valuable due to its darker than average base colour, meaning that all colours present appear more brilliant. This is because of the contrast that a dark background provides.
The pattern which the colours form also has an impact of value as well as which sub-type or classification the opal falls under. A common milky-white opal with a speckly pattern would be considered less valuable, while a pitch black opal with a multitude of strong, broad flashes of rarer colours would be considered a very high quality stone indeed. A gem quality opal also shows good colour even in dull light.
There are other important factors too and many of these are common among all gemstones. These include size and purity (whether or not traces of other minerals are present).
Rarity
All value is at least, partly, affected by supply and demand. Gemstone values are very much at the whim of these market forces. This is partly what gives these stones their allure. Rarity plays a major role in a stone’s value.
While opal itself is fairly common; precious, or gem quality opal is very rare. How is this possible? Well, its not that the materials that make up opal are actually uncommon. Its not even that the conditions for their formation are extraordinary.
Precious opals are rare because they must have a particular structure for them to appear the way they do. It is the formation of this structure and the presence of other nearby materials that make up a valuable opal.
This means that miners can find a seam of common opal and none of it will be gem quality. This makes precious opal finds very sporadic. Unless the opals in that seam formed the required structure there is no guarantee that the seam will contain any precious opal at all.
The end result of this is that the rarer forms of opal are even more scarce. There might be only one or two fields that produce a particular form of gem quality opal and some seams in that field will produce nothing. Due to this, some opals sell at prices that rival even the finest diamonds.
And once the mines that extract these rare types from run dry, there will be no supply of these gems until a new source is found. This is true for all rare variations of valuable stones and can dramatically increase value.
Large gem quality stones are exceptionally uncommon, particularly over 10 carats.
Hardness
Some competitors have discredited opals in the past due to their proclaimed ‘softness’. And while they are indeed less hard than diamond and even some of the other precious stones such as Ruby and Sapphire, opals are far more durable than some people might think.
For instance, diamond sits at 10 on the Moh’s scale of mineral hardness which is the highest point of the scale. Sapphire and Ruby are both at approximately 9 on the scale. These are all extremely hard gems.
Pure gold (24 carat) however is only 2.5 on the Mohs scale. This is why pure gold is rarely used for jewelry. Instead, 18 carat gold is considered suitable, even for use in rings. 18 carat gold sits at about 2.75 – 3 on the Mohs scale.
Platinum is even more valuable than gold and is in fact slightly harder. Platinum sits at around 3.5.
While these metals are not minerals, they are all far softer than diamond but are still considered suitable for jewelry if the owner takes care of it properly.
Opals range from approximately 6 to 7 on the Mohs scale, meaning they are significantly harder than the metals that they are usually set in. This is just slightly below the hardness of another common gemstone used in jewelry: emeralds. Emeralds are approximately 7.5 on the Mohs scale.
Clearly, these stones are softer than diamond, however, all jewelry needs to be treated with respect and care to avoid damage. 18 Carat gold is never questioned on its durability despite being vastly softer than opal.
Stability
Opals contain small amounts of water. This is due to the way they were formed. The water content of an opal can be anywhere between 3% and 21% by weight. A high percentage of water content can make an opal unstable. Stable opals have a water content as low as 3% to 10%.
If an opal is unstable, there is a chance for it to fracture and crack. However, after being mined, sorted, transported and cleaned, such flaws almost always present themselves.
Australian opals rarely exceed 6% water content and are therefore even less likely to crack. The Australian black opal is regarded as even more durable due to smaller molecules.
Australian opals are also non-porous, meaning they do not absorb water like other opals do i.e. Ethiopian opal.
Summary
All of this has an effect on value. A cracked stone might be only 10-20% of the value of a similar stone with no cracks. It also has an effect on the price of opals in general.
Opals are both more durable and rarer than most people think; Australian opals even more so. Many types of opal are even more rare than diamond and will only get rarer due to being found in only 1 or 2 places on Earth.