Boulder Opal is a unique variety of opal that is as its name suggests, found in “boulders”. Boulder opal consists of concretions and fracture fillings of precious opal, potch or common opal in a dark siliceous ironstone/sandstone matrix.
It is only found in isolated locations in western Queensland, from Kynuna in the north, to Yowah and Koroit in the south. The largest deposits are around Jundah and Quilpie in South West Queensland, and the Opalton area near Winton in the north.
Boulder Opals from different regions will have distinct characteristics and will often be named after the region where it comes from, such as Yowah nut rather than boulder opal.
Boulder Opal is mainly mined by open pit method, but can also be mined using underground techniques.
Boulder Opal is thought to have formed between 20 – 40millions years ago.
Boulder Opal has a MOH’s hardness of 5.5 – 6.5. It is most often cut into freeform cabochons for setting into pendants and other jewellery, but is also used extensively for beads, carvings and other ornamental uses.