Boulder opal

Boulder opal

The Koroit boulder opal rough is a famous stone to wear as jewelry rings, pendant, necklace, earrings or bracelet.

Buy natural boulder opal in our shop

Boulder opal is a rock that contains thin seams and patches of opal surrounded by or attached to its natural host rock. The cutter studies this rock and decides how to cut the best possible gem.

That gem might be cut to display seams and patches of opal as they appear within their natural host rock. Alternatively, the gem might be cut in an orientation that presents a thin seam of precious opal as the face of the gem with its natural host rock as a backing.


Opal is a hydrated amorphous form of silica (SiO2·nH2O), its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals.

It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt. Opal is the national gemstone of Australia.

Sample from Australia

Australian opal

The town of Coober Pedy in South Australia is a major source of boulder opal. The world’s largest and most valuable gem opal was found in August 1956 at the “Eight Mile” opal field in Coober Pedy. It weighs 17,000 carats and is 280 mm long, with a height of 120 mm and a width of 110 mm.

The Mintabie Opal Field located about 250 km north west of Coober Pedy has also produced large quantities of crystal opal and the rarer black opal. Over the years, it has been sold overseas incorrectly as Coober Pedy opal. The black opal is said to be some of the best examples found in Australia.

Andamooka in South Australia is also a major producer of matrix opal, crystal opal, and black opal.

Another Australian town, Lightning Ridge in New South Wales, is the main source of black opal, opal containing a predominantly dark background. Boulder opal rough consists of concretions and fracture fillings in a dark siliceous ironstone matrix.

It is found sporadically in western Queensland, from Kynuna in the north, to Yowah and Koroit in the south. Its largest quantities are found around Jundah and Quilpie in South West Queensland. Australia also has opalized fossil remains, including dinosaur bones in New South Wales, and marine creatures in South Australia

Koroit boulder opal

The Koroit opal field is an opal mining area in Paroo Shire in South West Queensland, Australia. It is located about 80 km north northwest of Cunnamulla.

It is not a town, nor should it be confused with the town of Koroit in rural western Victoria, Australia. It has neither electricity nor running water. Koroit is close to the town of Yowah which also produces a similar type of opal: the Koroit boulder opal

The Koroit boulder opal field is known for the very distinctive type that is found in its mines. In Queensland stone is found within a 300 km wide belt of sedimentary rocks in the Winton Formation. Here opal is found as a kernel in small concretions.

The Koroit Opal field was discovered in 1897 by Lawrence Rostron. The most recent mining events started in 1972 when the popularity and profitability of the stone increased. The mining is done by either open cut large scale mining or by underground shafts.

Boulder opal meaning and healing prperties benefits

The following section is pseudo scientific and based on cultural beliefs.

The gemstone has a pure energy, clears and strengthens the aura. Boulder opal rings provides clarity and purity of thought, un-cluttering a muddled and confused mind. The stone calms and centres, used in meditation can facilitate counsel with guides. It can help to reveal the inner truth of ones aspirations, ambitions and desires.

Opals activates the heart chakra and utilize wood energy, the energy of family and health, prosperity and abundance.

Boulder opal under microscope

We make tailormade boulder opal rough jewelry as rings, pendant, necklace, earrings or bracelet


Is boulder opal valuable?

They are not the most valuable type of opal (following black and fire opal). The stones, as the name suggests, are mined from large ironstone boulders under the ground.

What is special about boulder opal?

The stone typically displays bright and vibrant colors. The natural iron stone base gives added stability and adds to the depth of color produced in the gems. The varied and interesting natural shapes in which the gems occur make for added interest and unusual jewelry.

What is the difference between black opal and boulder opal?

Black opal often has a natural potch backing (colorless opal) on the back of the stone which also contributes to its dark body tone. For this reason, The stone is sometimes referred to as a natural doublet, as this layer of dark stone on the back gives the opal its dark body tone.

How can you tell a good quality opal?

To judge an opal, consider its play of color, body tone, brilliance, pattern, the thickness of the color bar, and any faults such as cracks or inclusions. Natural inclusions are acceptable but never buy an opal that’s cracked.

What does boulder mean?

In geology, a boulder is a rock fragment with size greater than 256 millimeters (10.1 in) in diameter. Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive. In common usage, a boulder is too large for a person to move.

How is boulder opal formed?

Formed in areas of Ironstone, gems are created when the host rock (Ironstone) forms as part of the opal when the gem is formed in cracks within the host rock. The resulting opal is often a thin vein laid on natural Ironstone.

Natural boulder opal for sale in our shop

We make custom made boulder opal as engagement rings, necklaces, stud earrings, bracelets, pendants… Please contact us for a quote.