Opal with grayish body color is referred to as semi-black opal. Found only in Australia (primarily at Lightning Ridge) these opals have a darker body tone than white but are not dark enough to be classified as black. The subtle body-color enhances the stone’s play-of-color and gives the gem a mysterious smoky appearance. Play-of-color can range in all hues of the spectrum. Opals are an October birthstone and are designated for the 14th wedding anniversary.