Opal

The opal is often called the Queen of Gems, and has been revered since the time of the Ancient Greeks and Romans, who believed it gave the holder the gift of foresight, or that it could protect from diseases and harm. The opal’s name comes from the Greek word opallus, meaning ‘to see a change in colour’. This colour shift is caused by diffraction within the opal as light his shifted within it.

The History of Australian Opal Mining
Australian produces 90-95% of the world’s opals, and Australian opal is seen as the best in the world. Though Australia has many opal mining towns, the major players are found in only three States: New South Wales, South Australia and Queensland. Opal fields tend to be dangerously hot, difficult climates to live in, requiring tough and determined miners.

Opals were first discovered in Australia in 1849, by a German geologist called Johannes Menge, near the small town of Angaston in South Australia. Opals were then found and mined in Queensland during the 1880s, and mining at White Cliffs in New South Wales began in 1890. Most of the early discoveries were accidental, and opal history is scattered with stories about horses kicking up rocks that carried opals, or a farmer’s wife finding a lovely rock in a creek bed.
Initially, opals were sent to Germany to be cut, but from 1900 onwards professional cutters came to the Australian opal fields, where they set up their homemade equipment to cut and polish the opals.

The incredible colours of Australian opals created a problem at the start, because Hungarian miners argued that Australian opals were fake, since such colours hadn’t been seen before. However, the authenticity was obvious as production continued. Australia soon became, and
remains today, the foremost producer in the world.

The Australian Opal Landscape
South Australia produces 50% of the world’s opals, mostly due to its place near the ancient Great Inland Sea, now known as the Great Artesian Basin or Great Australian Basin. The characteristics of this basin are vital to opal production, as it contains a vast amount of water, covering 1.7 million square kilometres of ground beneath Australian soil. The conditions it creates allows opals to form.

Lighting Ridge, the site of the NSW black opal production, is another large basin called the Surat Basin, which is also a part of the Great Australian Basin. The black opals found at Lightning Ridge are the most valuable form of opal, while the South Australian white opals are of lesser, yet still great, value.

How Opals Are Formed
The NSW and South Australian opals are formed similarly due to their basin locations. Opals form within host rocks, which are sedimentary rocks in horizontal layers that were formed by streams and rivers many millions of years ago. The opal itself is made from a mixture of water and silicon dioxide. Water moves down through the earth, collecting silica from sandstone as it goes. The water and silica then fills the cracks in the rocks that were caused by fossils or earth movement. As this happens over and over, the opal is slowly created.

Every opal is different and unique because each was formed in a slightly different environment, such as one with less water, slower moving water, or different rock layers. The Boulder opals from Queensland are formed somewhat differently to other opals, as they grow inside ironstone, filling between layers or in cracks. Because Boulder opal is attached to the ironstone, the opals are usually cut with the stone still connected, though if the opal is thick enough it may be cut from the ironstone. These Boulder opals can then be crafted into different shapes, however their freeform shapes are often kept to show the uniqueness of each.

Uses of Opals
Known as one of the five most precious gemstones, opals are up there with diamonds, rubies, emeralds and sapphires, and their primary use is in jewellery. Around 95% of opals are used for jewellery and ornaments, and these are valued for their colour and the range of designs within each gemstone. Opals are also used in gemstone therapy, or as focus points in some spiritual practices or money-related rituals.

Opal that is not of high enough quality for jewellery is used in brick, sewer-piping and ceramics, as well as in medicines due to its absorption properties. Opal can also be used in fertilisers and insulation, making it a very flexible and interesting gemstone.