Description Boulder Opals are mined in Queensland, Australia. They are precious opals usually inside of large Ironstone formations inside the Earth. These opals are characterized by their host rock, which is usually ironstone or sandstone. They are easily distinguished by their layer of solid brown ironstone left on the back of the stone. They’re the second most valuable opal behind black opal. This polished Boulder Opal is 3/4″ in length and 1/2″ wide.
