Australian Boulder opals are the second most valuable type of opal (following black opal). 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 forms in cracks and fissures in these boulders. Because these veins of colour 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 colour of the spectrum in a beautiful play of colour.
Size 8.5
3/4"x 1/4"