Although opals can be been found all around the world, there are only a few major sources of this gemstone. Australian opals account for 95% of the world’s supply. Unique geological formations in Australia have favored the formation of this sedimentary stone.
By Donald Clark, CSM IMG 2 minute read
Australian opals - Lightning Ridge

This freeform oval cabochon-cut opal from Lightning Ridge, Australia displays blue, green, and teal play of color. Long thought to be the result of iridescence, opal’s play of color (or “on-and-off” flashing of color) is actually the result of diffraction. © Dan Stairs Custom Gemstones. Used with permission.

The Great Artesian Basin

Great Artesian Basin - Australian opalsThe formation process began about 140 million years ago. At that time, an inland sea, abundant with silica-rich sands, covered much of central Australia. This sea eventually receded and formed what is now known as the Great Artesian Basin.

Around 30 to 40 million years ago, heavy weathering began to dissolve the silica. The holes that were formed in the rock began to collect silica-rich water. Over time, the silicates trapped in these spaces formed opals.

opal with broad flash

This freeform cabochon opal from Lightning Ridge, Australia shows a wonderful red, green, gold, and blue rolling ribbon-like broad flash pattern. © Dan Stairs Custom Gemstones. Used with permission.

Australian Opal FieldsWhile the Great Artesian Basin is vast, there are only a few sites in this area that are sources of opal. (As any miner will tell you, good quality opal is rare even in the best of areas).

On the map to the right, you can find notable Australian opal fields both within and beyond the Great Artesian Basin.

The Beginning of the Australian Opal Trade

The modern history of opal mining in Australia began in July of 1889. Tullie Cornthwaite Wollaston took 60 brilliant pieces of opal rough mined in Queensland to London.

Despite initial rejections from gem dealers, after Wollaston sold the stones to an international jewelry firm, the demand for Australian opals grew steadily worldwide.

Tullie Cornthwaite Wollaston

Mr. Tullie Cornthwaite Wollaston (opal dealer), ca. 1920. Photographer unknown. Photo is in the public domain.

Select Sources of Australian Opals

Today, most black opal (stones with a dark gray to blue-black background) comes from Lightning Ridge, New South Wales and Mintabie, South Australia. The fields around Coober Pedy, South Australia also produce some black opal.

Lightning Ridge Black Opal

8-ct Lightning Ridge black opal. Photo by Daniel Mekis. Licensed under CC By-SA 3.0.

Coober Pedy and Mintabie are also rich sources of light and white opal (stones with a white or light background).

Rainbow Shield Mintabie Opal Pendant

Rainbow shield Mintabie opal pendant. Photo by Dpulitzer. Licensed under CC By-SA 4.0.

Boulder opal, a thin seam of precious opal on an ironstone matrix, is found at a number of locations in Queensland. Smaller finds also come from Andamooka, South Australia.

Boulder opal, 2765 carats - Queensland, Australia

At 2,756 carats, this is one of the largest and finest-quality boulder opals ever mined. Opalville Mine, Queensland, Australia. Photo by gini. Licensed under CC By-SA 2.5.

Yowah nuts, walnut-sized stones with opals in the center, are found in Yowah, Queensland.

Yowah nut - Queensland

Yowah nut, Queensland, Australia. © Rob Lavinsky, www.iRocks.com. Used with permission.