Black Opal vs Boulder Opal

Australia is lucky to be the home of both the Black Opal and Boulder Opal. These amazing Opals are spectacular but do you know the differences between them? Read on to be enlightened..

Sometime between the 1880’s and 1890’s a discovery was made that proved to be a big find, and that was the discovery of the Black Opal in Lightning Ridge, Australia. Since its discovery the Black Opal has enjoyed growing fame in many different parts of the world.

It also has the reputation of being a very stunning Opal whose brilliance has made it one Opal that is highly sought after all over the world. The Black Opal is usually discovered via mining and is considered a very vibrant Opal compared to its South Australian counterparts.

In the 1870’s, Boulder Opal was discovered in Western Queensland, Australia and since then its popularity has continued to increase. It is currently ranked second on the list of valuable Opals. Despite its value and popularity within its locality it’s not really known to the international community.

Boulder Opal is formed in ironstone boulders where the precious Opal fills the cracks within the ironstone. Boulder Opal is found via mining and a lot of dirt has to be cut off from the surface to mine the Boulder Opal.

Opal Comparison

While both are amazing Opals they have properties that could be similar in some cases and different in others. Here’s my comparison on six important characteristics between Black Opal and Boulder Opal.

Pattern and Colour

Black Opal
Black Opal comes in various patterns including Chinese writing, harlequin, ribbon, floral, straw, and the colours vary, as it is able to display the colours of the rainbow brilliantly.

Boulder Opal
This is almost identical to the Black Opal in its colours, brilliance and patterns.

Body Tone

Black Opal
From its name ‘Black Opal’ it can be deduced that the name is attributed to the body tone which is dark and often times it ranges between black and dark grey. The darkness of the stone is a contributing factor to its brilliance. In most cases, the Black Opal comes with a potch backing found on the stone’s back and is also responsible for the opal’s body tone.

Boulder Opal
Just like the Black Opal, the Boulder Opal is also dark-toned; however, there are cases when Boulder Opals have white body tones. Because of the formation of the Boulder Opal in ironstone, the ironstone usually remains on the back of the Boulder Opal, hence the presence of a brown rock on the back of the Boulder Opal.


Black Opal
The hardness of the Black Opal is similar to the White Opal and according to the Mohs scale of hardness, the hardness is measured as between 5.5 to 6.5. This is compared to a Diamond whose hardness is measured as a 10 on the Mohs scale.

Boulder Opal
The Boulder Opal has a strength advantage over the Black Opal. The ironstone on the back of the Opal gives it more strength and extra hardness and this gives the Boulder Opal more advantage over every other type of Opal when it comes to strength. Hence, there is more resistance to external impact.


Black Opal
Based on market demands for the Black Opal, it is usually oval shaped, symmetrical and has a cabochon top that is domed in shape. This shape has also been popular in fashion over the years and has changed over the years depending on the demands of the jewelry industry.

Boulder Opal
Boulder Opals differ from the Black Opal in shape because of the Opal veins’ thin nature which makes it impossible to have dome-shaped cabochons. Hence, they are usually cut as irregular shapes or left in its free form. This is in a bid to retain more of the Opal. In contrast to the Black Opal, the Boulder Opal has a different target market, especially for jewellers that create jewelry with irregular shaped stones.


Black Opal
The Black Opal unlike other Opals is the rarest Opal available and can only be found in Lightning Ridge, Australia. The Black Opal is so rare that it cannot be found anywhere else in the world and its rarity keeps increasing.

Boulder Opal
This can easily be found in Western Queensland, Australia and within a 500-kilometre radius, unlike the Black Opal that is located just within a 70 km radius in Lightning Ridge, Australia. Hence, it can be said that the mining of Boulder Opals will be more profitable in the near future.


Black Opal
Due to the fact that Black Opal is very rare and valuable, it is a highly priced stone. The Black Opal is an item that is highly sought after and that is also another factor responsible for its high price. Furthermore the beautiful patterns and alluring color of Black Opal also contributes to its market cost. Basically the price and value of the Black Opal is determined by the simple market forces of demand and supply.

Boulder Opal
Boulder Opals are relatively cheaper than Black Opals, even though it costs more to mine Boulder Opals than Black Opals. The reason why this is so, may be due the fact that the boulder opal can hardly be cut into regular shapes, which makes it difficult for jewellers to use.

Final Words

With the comparisons made above, you should be able to easily differentiate between the Black Opal and the Boulder Opal. Opals are beautiful stones to behold and bring aesthetic value when used in jewellery. In terms of Black Opal vs Boulder Opal it will always come down to preference. Black Opal offers colors and patterns that are not seen in other gemstones. Combined with the rarity of this stone it truely is a remarkable gemstone. However Boulder Opal offers a unique and very affordable Opal that is both beautiful and one of a kind.

Over to you, which one will you choose?







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