Boulder Opals are the second most valuable opals in the world after Black Opals. They are characterised being a natural combination of solid opal and ironstone or in some cases fossilised wood. The opal formed within the cracks of the ironstone boulder, which when split shows a shiny and deep coloured opal faces against the dark brown stone.
Australian boulder opal come several opal fields within the wide area of outback Queensland, many have been given a unique name (eg. Yowah, Koroit, Quilpie, Opalton), which then relates to specific set of characteristics observed on the stone, like patterns, let it be a seam, or a networks of opal veins forming a matrix.
Host Boulders can vary in size from mm to meters, so an Opal boulder can be a cut of a very large boulder, however what we call Yowah nuts are mini boulders 5mm to 20cm which host an opal and specific to that region.
To help with selective viewing, you will find Koroit opals and Yowah Nuts in their own category due to their uniqueness. We also created a region filter to select areas like Yowah, other smaller opal fields may be mentioned in the stone detailed description along with patterns and colours.