Black Opal VS Boulder Opal

Black Opal VS Boulder OpalOpals are rare and breathtakingly beautiful. That explains why these are considered highly valuable gems. When it comes to determining the value of an opal, there are various factors to consider such as the type of opal, size & pattern, body tone, color bar thickness, and quality of the cut and polish. There are various types of opals available on the market and it can be a bit confusing to identify and comprehend the difference between them. Some of the most famous types of opal include Crystal Opal, Andamooka Opal, Dark Opal, White Fire Opal, Yowah and Koroit Opal, and smaller opal fields such as Tintenbar and Mintabie. However, two of the most sought-after opals are Black Opal and Boulder Opal. Many opal enthusiasts want to know the difference between Black and Boulder Opal. It is always fun to unfold which type of opal is better and more valuable. So, before we tell you which opal is more valuable and superior, it is best to know a little bit about them. Shall we?

Black Opal

The term “Black Opal” is used for opal that has a dark body color (it can be dark grey, black, dark blue or even dark green). It is one of the most popular types of opal on the market. The precious Black Opal is only produced by a famous town in NSW, Australia called Lightning Ridge. It was discovered in the area in the 1880s or 1890s, but at that time not many people were aware of its value. Today, it is widely considered as the most stunning opal in the world.

Boulder Opal

It was discovered in the 1870s in Western Queensland. Today, it is considered the second rarest opal in the world after Black Opal. It is formed along side another rock known as Ironstone. The Opal fields of Queensland produce most of this type of Opal. The amazing thing to notice with Boulder Opal is the presence of remarkable red ironstone within the Opal.

Which one is better: Black Opal or Boulder Opal?

Now that you briefly know about black and boulder opal, let’s get into details.

Stone Shape

  • Black Opal: Most of the black opals in the market are a symmetrical, oval shape. It is because this shape is most popular in jewelry. But you can come across a freeform opal as well because they are specifically cut to maximize the stone weight.
  • Boulder Opal: These opals cannot be cut and shaped like other opals because they only contain a thin layer of opal (veins). That is why these stones are normally cut into irregular, freeform shapes to ensure that maximum size to stone is achieved. 

Boulder Opal vs Black Opal

Body Tone

  • Black Opal: As the name suggests, it has a dark body tone that varies from black to dark grey. Due to its dark body tone, black opal display colors in a more vibrant way as compared to other opals. The stone has a natural layer of potch onto its back that plays a pivotal role in making its captivating dark body tone. 
  • Boulder Opal: It can be said that it has a dark body tone just like a black opal. Given the fact that it is formed in thin veins in ironstone boulders, the back of the stone shows the host ironstone. You can find a layer of brown rock at the back of Boulder Opal. Overall, it has a dark body tone that is quite similar to Black Opal. 

Black Opal VS Boulder Opal

Color and Pattern

  • Black Opal: It is known for displaying brilliant patterns of color. The play of colors in black opals is truly mesmerizing as all colors of the rainbow are displayed in an impeccable manner. It displays various patterns such as straw, floral, harlequin, rolling flash, ribbon, etc. 
  • Boulder Opal: The spectrums of color displayed by boulder opal are similar to black opal. All the colors of the rainbow are displayed by this stone just like black opal, but they vary from black opals when it comes to patterns. 

Black Opal VS Boulder Opal


  • Black Opal: On a Moh’s scale of hardness, Black Opal has a rigidity of 5.5 - 6.5 (white opal has the same hardness as well). Diamond has a hardness of diamond is 10. So, it can be said that it is a somewhat fragile stone. 
  • Boulder Opal: It has the same opal layer as black opal, but it gains extra strength and hardness from ironstone backing – it also provides it an edge over other types of opals. Hence, it is more likely to survive greater pressure and impact as compared to a black opal. 


  • Black Opal: When it comes to the rarest types of opal, black opal surely tops the list. After all, it is found only in the Lightning Ridge (a town in Australia) and within a 70 kilometers radius. This opal is considered extremely rare because it is only found in Australia and nowhere else in the world. 
  • Boulder Opal: It can be categorized as a rare stone but it is more readily obtainable as compared to its cousin, black opal. It is because the area that yields boulder opal stretches along a 200-300 kilometers radius and only a small portion of it has been explored. Hence, it can be said that it has a promising future. 


  • Black Opal: It is much more expensive than boulder opal due to two obvious reasons: status and rarity. Given the fact that it is a quite rare and sought-after stone, it has a higher price as compared to other types of opal. 
  • Boulder Opal: There is no denying that boulder opals are magnificent, but when it comes to their comparison with black opals, they lose the battle. As compared to black opals, they are under-priced. It is considered that it has 1/3rd the price at which black opal is sold in the market. It is mainly because these are not as rare and famous as black opals and not priced ‘per carat’ due to the natural ironstone backing. 

The Bottom Line

If you are wondering which stone is better, then you need to know that both of them are equal in quality. Black opal is more expensive because of the rarity factor, but boulder opal is equally good. In the end, it all comes down to your taste and value in a stone. If you feel more satisfied in owning a rare stone, then your obvious choice would be black opal. All in all, both stones are equally beautiful and charming.


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