The harlequin opal is by far the most sought after example of opal and the stone that all opal collectors and lovers wish to have. The most important sources of precious opal today are in New South Wales, South Australia and Queensland in Australia. Typically the quality of opal is determined by various factors including the background colour and play-of-colour. Black opals are more highly prized than white. Opals with a strong vivid play-of-colour are judged more valuable, with reds being one of the most desired colours.