.75" Green/Blue Iridescent Boulder Opal Cabochon

Boulder opals are a striking variety of precious opal that come out of Queensland, Australia. While Australia is known for their extravagant black precious opals, the boulder opal is surely giving them a run for their money. The majority of boulder opals are extracted from a Cretaceous stratigraphic layer that spans over 249,000 square miles in the heart of the Australian continent. Boulder opal is collected from a few small opal fields in the Quilpie, Winton, and Paroo Shires, with a very small deposit in New South Wales.

Unlike black opals, which primarily form in igneous vugs and cracks, boulder opals form in sedimentary ironstone concretions. Because of this, opals form in thin bands and streams that may be delicate by themselves. This is why boulder opal on the market it is often in association with its ironstone matrix for support. The upside is that the earthy chocolate brown of the ironstone contrasts nicely with the beautiful array of colors these opals appear in. This dark backing also enhances the color of the opal's body, creating a more contrasted play of color.

When it comes to caring for your boulder opal, it is rather simple: boulder opal is stable straight out of the ground and ready for display. The only thing to consider is limiting harsh light and exposure to sunlight. This is good practice for most minerals, but especially to ensure the longevity of your specimen's opalescence.