Australian Boulder Opal Ring Sz.8
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 colorful opal forms in cracks and fissures in these boulders. Because these veins of color are so thin, opal cutters need to leave the ironstone on the back of the opal to form a full sized stone. The thin layer of opal in boulder opals can display any color of the spectrum in a beautiful play of color.