Olympic Australis — The Largest Gem Opal Ever Discovered
Olympic Australis — The Largest Gem Opal Ever Discovered
A 17,000-carat South Australian gem opal recovered at Coober Pedy in 1956 and named for the Melbourne Olympic Games
The Olympic Australis is the largest and most valuable gem-quality opal ever discovered, a single mass of approximately 17,000 carats — about 3.4 kilograms — recovered at the Eight Mile opal field in Coober Pedy, South Australia, in 1956. The stone was named in honour of the Melbourne Summer Olympic Games of that year, the first Olympic Games hosted in the southern hemisphere, and remains a celebrated piece of Australian national patrimony. It is approximately 28 centimetres long, 12 centimetres wide, and 11 centimetres deep, displaying vivid play-of-colour across a substantial portion of its surface and considered to be approximately 99 per cent gem-quality opal — an astonishing proportion for a piece of this size.
The discovery
The Olympic Australis was unearthed by an Australian opal miner — accounts variously attribute the discovery to a single miner or to a small mining team — at a depth of approximately ten metres in the Eight Mile opal field at Coober Pedy. Coober Pedy, in the arid interior of South Australia approximately 850 kilometres north-west of Adelaide, is one of the world's most important opal-producing localities, and has been the principal source of fine Australian precious opal since deposits were first worked there in the 1910s. The Eight Mile field is one of several major mining areas around Coober Pedy.
The stone was found in a single rough mass rather than as multiple fragments, which is itself remarkable. Most large opal recoveries break apart during extraction or display only patchy gem material on a substantial common-opal matrix; the Olympic Australis combines exceptional size with unusual continuity of gem material throughout the mass.
Description and value
The Olympic Australis displays the play-of-colour characteristic of fine precious opal — the diffraction-based phenomenon by which the regular three-dimensional array of silica spheres in the opal structure separates white light into spectral colours that flash and shift as the angle of view changes. The stone shows particularly vivid red, green, and blue colours across substantial zones of its surface, with the gem material extending well into the interior of the mass rather than being confined to a thin surface layer.
The Olympic Australis was acquired by the Altmann & Cherny jewellery firm in Melbourne, where it has been held since shortly after its discovery and exhibited as a public display piece at the firm's premises. It has been valued at AUD 2.5 million in 2005 — a value considered conservative by some commentators given subsequent escalation in fine opal prices — and would today command substantially more in any open-market transaction. The stone has not been cut into individual gems, which would have produced perhaps a dozen large fine opals and many smaller ones; the decision to preserve it as a single mass reflects the recognition that the Olympic Australis is more valuable as an intact specimen than as cut stones.
Significance
The Olympic Australis is significant in three principal ways. First, as the largest gem-quality opal ever recovered, it represents the upper bound of what the geological processes that produce precious opal can deliver, and stands as a benchmark against which all subsequent large opal discoveries are measured. Second, as a symbol of Australian national patrimony and of the country's position as the dominant source of precious opal — Australia produces approximately 95 per cent of world fine opal supply — the stone has substantial cultural and symbolic value beyond its purely gemmological character. Third, as a public display piece exhibited continuously since 1956 at Altmann & Cherny's Melbourne premises, the Olympic Australis has functioned as a focal point of Australian opal awareness and tourism for nearly seven decades.
The Coober Pedy field
The discovery of the Olympic Australis can only be understood in the context of the Coober Pedy field's geological setting. The field lies in Cretaceous sedimentary rocks of the Great Artesian Basin, where ancient lakes and seas deposited sandstones and claystones that subsequently host the world's principal precious opal deposits. The opal forms by the slow precipitation of silica from groundwater into voids in the host rock — fossil shells, fractures, root cavities — over geological timescales of millions of years. The conditions necessary for fine opal formation are exacting, and most opal-bearing host rock contains only common opal without the regular silica-sphere ordering that produces play-of-colour. The Olympic Australis represents an exceptionally favourable convergence of conditions that produced gem material across an unusually large mass.
In display and the contemporary trade
The Olympic Australis remains held by Altmann & Cherny and on public display at the firm's Melbourne showroom in Bourke Street. It has not changed hands in private sale and is not available for purchase. Other major Australian opals — the Galaxy, the Andamooka Opal (the Queen's Opal presented to Queen Elizabeth II in 1954), the Aurora Australis — occupy related positions in the canon of important Australian opals, but the Olympic Australis is generally accorded the first place by both size and continuous-gem proportion.