Comparative analysis of sedimentary and volcanic precious opals from Australia

Australasian Ceramic Society
Publication Type:
Journal Article
Journal of Australasian Ceramic Society, 2008, 44 (2), pp. 17 - 22
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Precious opal is Australia's national gemstone with Australian opal fields providing 90% of world production. The sedimentary geological environment associated with Cretaceous sediments of the Great Artesian Basin is the source of most precious opals in Australia. The deposit of precious opal at Tintenbar in northern NSW is the only kwnon commercial occurrence of precious opal in volcanic environment in Australia. Differences in silica structure of opal previously classified by x-ray diffraction (XRD) in the 1960's by Jones and Segnit identified three types of opal structure - amorphous opal-A, opal-CT with a porrly crystalline intergrowth cristobalite and tridymite and opal-C shwoing the cristibalite structure.
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