Australian opal is a type of precious opal that is found primarily in the southern and central parts of Australia. It is known for its unique play of colors, which are caused by the diffraction of light by the small silica spheres within the stone. The colors can range from red, orange, yellow, green, blue, and purple, and can be found in a variety of patterns including pinfire, harlequin, and flash.
Australian opal is formed in a variety of ways. The most common type is called "nobbin opal" which forms in sedimentary rock such as sandstone, and is usually found in the form of small nodules. Another type is called "seam opal" which forms in cracks or crevices in the rock, and is often found in the form of thin veins.
Australian opal is graded based on the intensity and brightness of the play of colors. The most valuable opals are those with a strong play of colors and a high degree of color change. The less valuable opals are those with a weak play of colors or little color change.
Australian opal is a popular choice for jewelry because of its unique beauty and rarity. It is used to create a wide range of jewelry items including earrings, necklaces, bracelets, and rings. However, care should be taken when caring for opal jewelry as it is a delicate stone and can be easily damaged if exposed to extreme temperatures or harsh chemicals.
Overall, Australian opal is considered a unique and beautiful gemstone, prized for its play of colors and rarity. It is an ideal choice for those looking for a special and unique piece of jewelry.
One notable study on Australian opals is "Opal-A" by J.B. Jago, which describes the geology of opal deposits in Australia and provides information on the different types of opals found in the country, including nobbin opal and seam opal.
Another study is "Opal from Lightning Ridge, New South Wales, Australia: A review of its geology, mineralogy, and genesis" by R.J. Bodnar and J.B. Jago which describes the geology and mineralogy of opals found in Lightning Ridge, New South Wales, which is one of the most famous areas for opal mining.
It is also worth noting that, Opals are fragile and sensitive to heat, light and strong chemicals, so it's important to be well informed about how to care for opal jewellery.
In general, more research can be found by searching for academic journals or articles on geology, mineralogy, and gemology that focus on Australian opals.