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Boulder Opal

What is boulder opal? Where is boulder opal found? How is boulder opal mined? How is boulder opal cut? How is boulder opal valued? Are there different types of boulder opal? FAQ: Would a boulder opal be suitable for an engagement ring?

Boulder Opal is a type of Australian opal that is found in Queensland. The key defining feature of boulder opal is the host rock the opal is found in.






Boulder Opal is found in the cracks and crevices of large weathered boulders that once lay on the ocean floor and as concretions with ironstone fed from fissures and faults.  The opal formation event took place one hundred million years ago at the end of the Jurassic (dinosaurs) and the beginning of the Craterous period (high sea levels). During the Craterous period, three quarters of the Australian continent was under water.


When you visit the opals fields today you are standing on what was once an ocean floor.

Opal appears in many places all over the world but Australian opal is the most highly regarded for its beauty, diversity and stability.

Australian Opal is sometimes referred to as the Queen of Gems.

Boulder opal has its own particular properties and although it is related to black opal and white opal through shared opal structure, the existence of host rock makes boulder opal distinctively different.


Mining Boulder Opal


Boulder Opal is either mined open cut using heavy machinery or in shafts and drives (holes and tunnels usually dug by hand).

Having good contacts are very important when it comes to buying opal. Dealers wishing to buy opal get on the telephone and ring around before they embark on a trip to the opal fields. Miners have their own networks and know who’s got what and who’s good to deal with and who’s not. If the buyer thinks there’s a good chance to buy a ‘parcel’ they’ll drive thousands of kilometers (in haste) to pick that parcel up.

Boulder Opal miners generally don’t go to market; the market comes to them.

Opal is an exhaustible resource and with fewer people mining and little being found its no surprise that parcels of rough opal are snapped up by eager buyers as soon as the opal comes out of the ground.

Cutting Boulder Opal


Boulder opal is cut using saws, grinders, sanders and polishers.

How rough boulder opal is cut is determined by the value of the opal.

If the opal is gem grade it is approached with extreme caution. Nothing is sacrificed, every vein is chased. When veins are thin, cutters use hand drills to gently remove the rock from the opal vein to expose the color. Skilled opal cutters are prized for their ability to produce a good yield.

Cutting boulder opal specimen grade is different. Learn more about valuing opal here.

Specimen grade is usually very artistic and lends itself to being cut into large interesting pieces that may depict landscape scenes or natural works of art.  As specialist in cutting boulder opal we use this grade to cut the beautiful boulder opal jewelry in the Opal Art scenic range.

Sometimes cutters will break a large boulder specimen (opal rock) down into smaller boulders. They do this by gently tapping the rock with a hammer to see if they can break it along natural cleavages. If a cleavage presents, the boulder comes apart and a “split” is produced. Splits are ideal for making earrings.



Boulder Opal Value

Boulder Opal is valued on carat weight and piece price.

Gem grade boulder opal is sold by carat weight. Lower grade boulder opal is sold by piece price.

Price is related to rarity of color, pattern and size.

Red is the rarest color followed by green then blue being more common.

Black Boulder is a grading term that describes the top grade of Boulder Opal.

Pricing is done through grading.

Grading is done by experts.

Once graded the final pricing is set by the market.

If opals are in short supply the price goes up.


Quality Terms Use Value
Gem/vein opal/precious opal Distinct pattern and rich colour. Precious opal exhibits the phenomenon known as 'play of colour'. Jewellery Investment
Scenic/picture stones
Image provoking. Combination of ironstone and opal. Precious and common opal present together. All jewellery lines, polished specimens Subjective value
Potch/common opal Opal that does not exhibit 'play of colour'. Polished specimens, carvings and ornaments Subjective value


Types of Boulder Opal.  

Australian Opal is usually named after its origin.

Winton Boulder Opal

Winton boulder opal is known for its hard ironstone host rock. Winton is the dinosaur capital of Australia. The host rock of the Winton Boulder Opal is rich in iron. This makes the boulders that carry the veins of opal dense and hard to cut but beautiful to finish.



Quilpie boulder opal is found in either sandstone or ironstone.  The opal from these fields is broad ranging in appearance. The opal can be vastly different from deposit to deposit. The Quilpie fields have had periods of great production. In the 1970s huge amounts of opal was found in the Quilpie region and these finds were pivotal in establishing the modern opal industry. Boulder Opal was first mined commercially at Listtowel Downs, near Quilpie in 1875.


Matrix opal

Matrix opal is another type of boulder opal. Matrix opal is ironstone containing the most brilliant array of pin size specs of color. The colors of matrix opal can be green, blue, purple and sometimes red. Matrix opal is sought after for bead making and slabbing.



Crystal Opal or Pipe Opal

Crystal Opal is a type of boulder opal. As the name suggests the opal forms in ‘pipes’ in the host rock which is usually sandstone. The sandstone in which the pipe opal has lay down is light and porous making it easy to remove and cut ‘clean stones.’ A clean stone is an opal gemstone that has no rock on the opal face. Crystal opal is a ‘pure’ form of opal.

Pipe opal is prized for its delicate, complex color patterns and pure form.


Yowah Opal

Yowah opal is another type of Boulder Opal. Yowah opal is characterized by fantastic intricate opal patterns in rock. Yowah opal is easily identifiable and lends itself to artistic jewelry design.



Koroit Opal

 Koroit opal is beautiful, rare and highly prized. The Koroit fields are near Yowah yet the opal is very different. So little opal comes out of the Koroit fields it is hard to find any for sale.



Boulder Opal Jewelry

Boulder Opal is suited to designer hand made jewelry. Boulder Opal is usually cut free shape and requires setting. For those wishing to make something special in metal (silver or gold) a jeweler will take on the commission, help design and quote on making the jewel. For something more organic a hole can be drilled in the opal and either worn free style (like many of the pendants in our range) or fixed to a silver top to accommodate a chain.



FAQ: Would a boulder opal be suitable for an engagement ring?

Because opal is not a hard stone it does not lend itself to being worn all the time. After being exposed to the rigors that hands encounter every day an opal will eventually give in and scratch, chip or break if worn all the time every day.

If the wearer understands the risks of wearing an opal all the time, but still wants an opal engagement ring we would say, “go ahead, but wear with care.”

For a boulder opal engagement ring we recommend the jeweler set the opal gemstone into a bezel setting.

A bezel setting protects the opal by capturing the edge of the opal gemstone in the metal setting and raising the setting above the gemstone to clear it from direct contact with the outside world.