Opal:
Opal stone has been a mystery for centuries. No two opals look the same. The word "opal" was derived from the Greek word opallos, meaning "to see changes in color." Opal is derived as a rare gemstone that is formed from non-crystalline silica gel. It is composed of 6 to 10 percent water, and small spheres of silica are arranged in a regular pattern. It generally measures 5.5 to 6.5 on the MOH hardness scale with diamonds measuring 9 to 10 and pearls 4 to 5. It is the stone for October.
The opal bracelet dates back to 1849 when it was found on the Tarrawilla cattle station near Angaston about 80 km from Adelaide, Australia. Almost 95% of opal is found in Australia. A small number are found in other countries such as Mexico, Brazil and the USA. There are three main opal mining areas in Australia that produce different types of opal.
The most famous opal is the black opal found in Lightning Ridge, New South Wales. Boulder Opal is located in Central Queensland, Quilpie, Winton and Opalton. Other opals include light opal, doublet, triplet, plain, synthetic, and imitation.
Most of the opal deposits are located in New South Wales, South Australia and Queensland. Currently, opal is mined in the following areas, each producing solid opal with specific characteristics and color patterns.
Lightning Ridge, NSW, is famous for its beautiful black opal. This city is located 770 kilometers northwest of Sydney. Black opal was first discovered at Lighting Ridge in the late 1880s.
White Cliffs is Australia's oldest commercial opal field. It is located about 295 kilometers northeast of Broken Hill. Opal was first mined at White Cliffs around 1889. For nearly 30 years, the White Cliff Opal Fields produced opal for the world market.
The real development of the vast opal deposits in Queensland began in 1873 with the discovery of fine opal north of Thargomindah. Opal mines are concentrated in certain areas such as Yowah, Quilpie, Eromanga and Jundah.
Coober Pedy is famous for its white or milky opals. Currently, the opal fields cover an area of approximately 45 kilometers. Andamooka is located southwest of Coober Pedy in rugged desert country. Andamooka is one of Australia's most famous opal fields, having produced some of the most beautiful pieces of opal. The opal fields in and around Andamooka produce top quality gem, crystal, light opal and some dark opal.
Opal is usually found in both sedimentary and volcanic rocks. There are different ways to mine opal.
Opal mining methods
Sink the shaft:
The simplest form of opal mining is digging a shaft with a pickaxe and shovel. The shaft sinks straight down until the promising "opal dirt" appears. The length of the shaft can be as short as three meters or as long as 20 meters. A hand toothpick or screwdriver is used to extract any opal found due to the fragility of the stone.
Open pit mining:
The open cut method is performed using heavy machinery to remove large amounts of opal impurities from closer to the surface for inspection. This method is more expensive and is mostly used to find boulder opal in Central Queensland.
noodle:
Many locals search piles of discarded mullocks for pieces of precious opal. An abandoned open pit mine is another good spot for noodles, using the rake and sieve for tools. Some have opted for machine noodling on a large scale by allowing large amounts of opal impurities to travel on a conveyor belt under an ultraviolet light that detects the rare fire opal.
Puddling and rumbling:
A puddler is a large net-lined drum attached to an engine. This device rotates and turns the clay into sludge as water is pumped into the drum. Sludge escapes through the mesh. A related technique is dry booming.