Dimensions: 21.70 x 24.20 x 4.68mm
 
Australian boulder opal is a type of opal that is found in the boulder matrix rock in Queensland, Australia. Unlike traditional opals, which are often found in solid form or as opal "nobbies," boulder opals are formed within the cracks and seams of ironstone or other types of host rock. The opal deposits are naturally integrated with the host rock, which can give the opal its distinctive appearance, often with vivid colors and intricate patterns.