Across the world, precious opal occurs in very few locations because it required a very special series of geological, climate and possibly biological phenomena to coincide for opals to form. These special criteria occurred in what is now the great desert regions of central Australia, which produces around 90% of the world's precious opal.
Opals are formed from a solution of silicon dioxide and water. As water runs down through the earth, it picks up silica from sandstone, and carries this silica-rich solution through cracks and voids caused by natural faults or decomposing fossils. As the water evaporates, it leaves behind a silica deposit. This cycle repeats over very long periods of time, and eventually opal is formed.
Music: Tibetan bell & Sounds from Outer Space Uranus V 2 06 - The real Horst (by special permission.) Remix by Leo Bar; The Ancients - Celestial Aeon Project :: jamendo.com/en/track/25388/the-ancients - Attribution-NonCommercial-ShareAlike 3.0 Unported (CC BY-NC-SA 3.0)
[sources: nationalopal.com/opals/precious-opal-formation.html - mindat.org/ ]
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