Discover Australia's ancient inland seabed and Andamooka's famous opalised fossils. Explore different types of minerals, stones, and gems, learn about the formation of opal, what to look for and how ...

This separates it from sugar-acid treated opal (Winter 2011 GNI, pp. 333–334), where the darker color is confined to a more or less thick surface layer. Initial X-ray fluorescence analyses showed ...