Comparative Analysis Of Sedimentary And Volcanic Precious Opals From Australia

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 New South Wales is the only known commercial occurrence of precious opal in volcanic environment in Australia. This paper examines the differences between sedimentary precious opals from Coober Pedy, S Australia, and volcanic precious opal from Tintenbar, NSW using XRD, SEM and thermal analysis.