Boulder Opal Statement ring with patterned band sz 7.5Amazing Boulder Opal with a beautiful purple river throughout. Set in sterling and fine silver with a fern patterned band. Size 7. 5 **Australian Boulder opals are easily distinguished by their layer of solid brown ironstone left on the back of the stone. Boulder opals, as the name suggests, are mined from large ironstone boulders under the ground. Thin veins of colourful opal form in cracks and fissures in these boulders. The layers of opal in