Precious Opal is an unusual mineraloid with a high content of water part of its natural constitution. Welo produces variety of beautiful opals including precious opal, fire opal and black opal. ![]() Until 10 years ago, Australia was still the dominant supplier of rough but Ethiopia has become an important source of Opal, sometimes called Welo Opal, named after the province of Ethiopia. There are two main sources for gem-quality opal, Australia and Ethiopia. Other localities in Australia produce a huge variety of different types of opal including precious white opal from Andamooka, crystal opal from Coober Pedy and boulder opal from several localities. It generally has a body color that is blue to dark grey or black, with striking plays of color. Black Opal comes exclusively from Lightening Ridge, NSW, Australia and is the most expensive form of opal on average. Opal was first mined commercially at Listow Downs in Queensland starting in 1875 and later in New South Wales, Australia. The more uniform the structure of the spheres, the higher quality of color-play produced. Later spheres created yellow, orange and red colors. When viewed under a microscope, scientists discovered that when these spheres are smaller they produce violet, indigo and blue colors. This material from into a gem like material that slowly hardened and formed into veins of opal. Much of the silicon-rich deposits came from organic material like diatoms, a tiny form of algae. Each gem-quality opal is made up of millions of tiny silica spheres that are arranged in a fairly regular pattern. Opal is formed by the slow seep of silicon-rich water seeped into voids left by fossils, volcanic vughs and any cracks that this pressurized liquid could deposit itself. When examined under a microscope, Opal has microscopic spheres that create the play of color called opalescence. The internal structure of gem quality Opal causes it to diffract light, causing a play of color, which can display virtually all colors from blue, to pink, green, yellow, white and black. Opal is a hydrated amorphous silica, meaning it naturally contains a significant amount of H2O, from a minmum of 3% up to 21% by weight.
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