What is the rearest type of opal?

The rarest type of opal is the black opal, particularly those that originate from Lightning Ridge in Australia. Black opals feature a dark body tone that enhances their vibrant play-of-color, making them highly sought after by collectors. Other rare types include white opal with a unique play-of-color and boulder opal, which is formed within ironstone rock. Overall, the combination of color, clarity, and origin significantly impacts their rarity and value.