Boulder opal

The Koroit boulder opal rough is an exquisite gemstone, perfect for use in various types of jewelry such as rings, pendants, necklaces, earrings, and bracelets. Known for its vibrant colors and unique patterns, it is highly cherished by both gem enthusiasts and jewelry designers.

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Boulder opal is a fascinating stone that contains thin seams and patches of opal embedded within or attached to its natural host rock, typically ironstone. The cutter carefully studies each piece of boulder opal rough to determine how best to maximize its potential, resulting in gemstones that highlight the unique beauty of both the opal and its natural host.

Some boulder opals are cut to display opal seams and patches within their natural host rock, creating a striking contrast between the vivid opal colors and the earthy tones of the surrounding rock. In other cases, the cutter may orient the opal to present a thin, colorful seam as the primary face of the gemstone, with the host rock serving as a sturdy and complementary backing. This process enhances both the visual appeal and the durability of the finished stone, making boulder opal a versatile and popular choice for jewelry.

Opal

Opal is a hydrated amorphous form of silica (SiO2·nH2O), with a water content ranging from 3% to 21% by weight, though it is most commonly between 6% and 10%. Due to its lack of a defined crystal structure, opal is classified as a mineraloid, in contrast to crystalline forms of silica, which are considered true minerals. Opal forms at relatively low temperatures and can occur in the fissures of nearly any type of rock, but it is most commonly associated with limonite, sandstone, rhyolite, marl, and basalt. Opal is notably the national gemstone of Australia.

Sample from Australia

Australian Opal

Australia is a renowned source of opal, with numerous regions known for their distinctive varieties. The town of Coober Pedy in South Australia is one of the most famous opal mining areas and a major source of boulder opal. The world’s largest and most valuable opal, weighing 17,000 carats, was discovered in Coober Pedy in August 1956. It measures 280 mm in length, 120 mm in height, and 110 mm in width.

The Mintabie Opal Field, located about 250 km northwest of Coober Pedy, is known for producing large quantities of crystal opal and the rarer black opal. Over the years, much of the opal mined here has been erroneously marketed as Coober Pedy opal. Despite this mislabeling, the Mintabie opals are known for their exceptional quality, with some of the best black opals found in this region.

Andamooka, another opal mining region in South Australia, is famous for its matrix opal, crystal opal, and black opal, each showcasing unique characteristics and stunning colors.

In New South Wales, the town of Lightning Ridge is the principal source of black opal, a highly sought-after variety characterized by its dark background, which provides a stunning contrast to the vivid play of colors within the opal. Boulder opal rough from Queensland often contains colorful opal concretions and fracture fillings set within a dark ironstone matrix, creating a striking visual effect.

Boulder opal is found sporadically across western Queensland, with significant deposits located from Kynuna in the north to Yowah and Koroit in the south. The largest quantities of boulder opal are extracted from the regions around Jundah and Quilpie in South West Queensland. In addition to these deposits, Australia is also home to opalized fossils, including dinosaur bones in New South Wales and marine creatures in South Australia, providing a fascinating glimpse into the country’s prehistoric past.

Koroit Boulder Opal

The Koroit opal field, located in Paroo Shire in South West Queensland, is a notable opal mining area renowned for its unique and distinctive type of boulder opal. The field is situated approximately 80 km north-northwest of Cunnamulla. It is important to note that Koroit is not a town, and should not be confused with the town of Koroit in western Victoria, Australia. The opal field lacks basic infrastructure such as electricity and running water but is relatively close to the town of Yowah, which also produces a similar type of opal.

Koroit boulder opal is known for its intricate and mesmerizing patterns, often featuring swirls and vibrant flashes of color embedded within the ironstone matrix. In Queensland, boulder opal is found within a 300 km-wide belt of sedimentary rocks belonging to the Winton Formation. The opal is commonly found as a kernel inside small concretions, creating a unique and visually striking gemstone.

The Koroit opal field was first discovered in 1897 by Lawrence Rostron. However, it wasn’t until 1972 that renewed interest in opal mining led to an increase in the popularity and profitability of Koroit boulder opal. Mining in the Koroit opal field is conducted using both large-scale open-cut methods and underground shafts, depending on the geology and the availability of resources.

Boulder Opal Meaning and Healing Properties

The following section is pseudoscientific and based on cultural beliefs.

Boulder opal is believed to possess a pure and calming energy, capable of strengthening and cleansing the aura. It is said to help bring clarity and purity of thought, un-cluttering a confused mind. Wearing boulder opal jewelry, such as rings, can promote a sense of tranquility and centeredness, making it a popular choice for meditation and spiritual practices. Some believe that boulder opal can facilitate communication with spiritual guides, revealing the inner truth of one’s aspirations, ambitions, and desires.

In terms of chakra work, boulder opal is associated with the heart chakra, and it is thought to help activate this energy center. The stone is also believed to harness wood energy, which symbolizes family, health, prosperity, and abundance.

Boulder Opal Under the Microscope

Customized Boulder Opal Jewelry

We create custom-made boulder opal jewelry tailored to your preferences. Whether you’re interested in rings, pendants, necklaces, earrings, or bracelets, we can design a piece that showcases the natural beauty of this stunning gemstone. Boulder opal’s unique patterns and vivid colors make it a versatile and captivating choice for personalized jewelry, perfect for special occasions or as a treasured gift.

FAQ

Is boulder opal valuable?

Boulder opal is not the most valuable type of opal compared to black opal and fire opal, but it is still highly sought after for its unique characteristics. Boulder opal is mined from large ironstone boulders beneath the ground, and the vibrant play of colors and intricate patterns make it a popular choice for jewelry.

What is special about boulder opal?

Boulder opal is prized for its bright, vibrant colors, which often appear against the dark backdrop of the natural ironstone base. This natural backing not only adds stability to the gemstone but also enhances the depth of color. Additionally, the varied and interesting natural shapes of boulder opal make it a unique and intriguing gemstone for use in jewelry.

What is the difference between black opal and boulder opal?

Black opal typically has a natural potch backing (colorless opal) that contributes to its dark body tone, whereas boulder opal forms directly within its ironstone host rock, which serves as the backing. Due to this, boulder opal is sometimes referred to as a “natural doublet,” as its dark backing enhances the stone’s body tone and overall appearance.

How can you tell a good quality opal?

To judge the quality of an opal, consider factors such as the play of color, body tone, brilliance, pattern, thickness of the color bar, and any faults like cracks or inclusions. Natural inclusions can be acceptable, but it’s important to avoid opals that show visible cracks, as these can weaken the stone and affect its longevity.

What does “boulder” mean?

In geological terms, a boulder is a rock fragment larger than 256 millimeters (10.1 inches) in diameter. Smaller rock fragments are referred to as cobbles or pebbles. In common usage, a boulder is often too large for a person to move manually, though smaller boulders can be rolled or moved with effort.

How is boulder opal formed?

Boulder opal forms in areas rich in ironstone, where silica-rich water seeps into cracks and voids within the host rock. Over time, the water evaporates, leaving behind the silica, which gradually forms opal. The resulting gemstone is often a thin vein of opal that is naturally bonded to the ironstone host, creating a visually stunning contrast.

Natural Boulder Opal for Sale in Our Shop

We offer a wide selection of custom-made boulder opal jewelry, including engagement rings, necklaces, stud earrings, bracelets, and pendants. To create your own unique piece of boulder opal jewelry, please contact us for a quote.