Seen as a symbol of love and hope in ancient Rome, the Romans gave this remarkable gem its name, Opalus, a Latin term tantamount to precious stones. In AD 75, Pliny the Elder, the Roman scholar, observed the kaleidoscopic qualities of this extraordinary gemstone. He noted how it encompassed the rich colours associated with other rare gemstones such as ruby, sapphire and emerald. The outstanding beauty displayed by the variety of colours found in rare black opals rivals the attraction of the traditional precious gemstones.
Although scientists believe that the majority of opal deposits were formed up to 30 million years ago, it is thought that opals found in Mintabie, one of Australia's main opal sources, could have been formed approximately 400 million years ago. In 1902 miners at Lightning Ridge discovered a new kind of precious opal that had a darker background colour than had ever been seen before. As a result, Australia became the centre of world opal production, which it still holds claim to today. The Lightning Ridge mine is still the leading source of black opal.
Three attributes combine to give an opal its unique splendour:
• Colour - Background colours and play-of-colour
• Pattern - Arrangement of play-of-colour
• Clarity - Transparency and amount of inclusions
An individual opal can differ greatly from another in appearance and quality. Even a single stone can change appearance by displaying a shift-of-play in colour and pattern. This can depend on a variety of different factors including: the time of day, the weather, lighting and viewing angle.
In black opals their background colours can vary between rich, dark shades of black, grey, blue, green or brown, but when viewed in reflected light they must appear black to be given the name black opal. The darker the background colour of a black opal, the more valuable the stone is. The premium qualities of the stunning black opal's intense background colour emphasise its play-of-colour making it even more desirable than lighter opals.
Opal is formed when the dry grounds are showered in heavy seasonal rainfall. The dry ground soaks up the water, carrying dissolved silica down into the ancient underground rock cavities. When the dry season comes back round the water evaporates from the heat of the burning sun, leaving behind the opals formed from silica deposits.