ADV Education

The Birth of Opal

Precious opals were formed in the distant geological past when an inland sea covered much of the eastern half of the Australian continent. During the Cretaceous period, dinosaurs roamed the shallow seas, and their remnants are now fossilised in the outback. Remarkably, some of these dinosaur fossils have transformed into precious opal, making opalised fossils a unique and significant part of Australia’s natural history.

Australia's Indigenous landowners spoke of opals in their Dreamtime legends of creation. It is easy to see why, in some Aboriginal folklore, opals are associated with the rainbow, the Rainbow Serpent, and Dreamtime spirits and creators.

European history also illustrates the enduring allure of opals. The famous Nonius Stone, owned by the Roman senator Nonius, was so cherished that he refused to sell it to Mark Antony, who had desired it for Cleopatra. In his Roman treatise on gemstones, Natural History, Pliny the Elder praised opals with one of the earliest and finest descriptions: “In opal, you will see the splendour and brilliant fire of ruby, the glorious purple of amethyst, the sea-green of emerald—all these colours glittering together in an incredible way.”

Today, opals are mined in three Australian states: New South Wales, Queensland, and South Australia. Lightning Ridge, NSW, is world-renowned for its exquisite Black Opals and fine Crystal Opals. Boulder Opals from Queensland captivate with their complexity and brilliance, while Andamooka and Coober Pedy in South Australia yield some of the finest Crystal and White Opals.

Australian history also celebrates Tully Wollaston, a pioneer of the opal trade. In the late 19th century, Wollaston travelled through the outback, trading opals and documenting his adventures, cementing his place as the father of Australia’s opal industry.

Precious opal is, without doubt, Australia’s national gemstone. Black Opal serves as the state gemstone emblem of New South Wales, while South Australia honours precious opal as its state gemstone.

Factors Determining the Value of Opals

The value of an opal is determined by several key factors:

• Brilliance: The brightness of an opal’s play-of-colour is paramount; higher brightness translates to higher value.
• Darkness: A black or dark background enhances the play-of-colour, contributing significantly to an opal’s value.
• Pattern: Unique patterns, combined with brilliance, can dramatically increase value.
• Colours: The number and vibrancy of colours affect value. While red hues are often the most sought after, brilliance and pattern remain more critical.
• Shape: Cabochons with high domes are generally more valuable than flatter stones. Freeform shapes, often seen in Boulder Opals, lend themselves to unique jewellery designs.
• Inclusions: Natural inclusions may reduce value, but some irregularities, like sand in the back of the stone, can assist in identification without significantly affecting value.

Types of Opal

Natural Australian precious opals are categorised by type and body tone:

• Black Opal: Found primarily in Lightning Ridge (NSW), these opals display vivid play-of-colour against a black body tone, making them rare and highly prized.
• Crystal Opal: Translucent or transparent, with brilliant colours that appear to come from deep within the stone. Found across Australian fields.
• Boulder Opal: Naturally attached to its ironstone host rock, Boulder Opals are known for their stunning colours and patterns, often rivaling Black Opals in brilliance.
• Matrix Opal: A unique form where opal is intricately diffused within the host rock, often ironstone or sandstone.

Other types include composite opals like doublets and triplets, as well as synthetic and imitation varieties.

Caring for Your Opal

Opals, while durable, require proper care to maintain their beauty:

• Natural Opals: Clean gently with a soft toothbrush and mild detergent. Avoid harsh chemicals or ultrasonic cleaners.
• Doublets and Triplets: Prolonged water exposure can cause separation of layers; clean with a damp cloth instead.
• Storage: Store opals in padded cloth bags. For extended periods, wrap them in cotton wool with a few drops of water in a sealed plastic bag to prevent drying out.