Black opal is considered the most valuable of opal varieties. Black opal contains traces of iron oxide and carbon elements not found in other common opals. These combined elements give black opal the unique color properties it is famed for. Black opal is mainly found in Lightning Ridge of NSW, Australia. In 2008, New South Wales declared Black opal as its Official State Gemstone.
Ethiopia is also known to produce treated black opal. The Ethiopian black opal is treated with a smoking process that darkens the color of the opal. The treatment enhances the play of color, rivaling some of Lightning Ridge's opals. The treated Ethiopian black opal is a great value gem because it sells for much less than Australian black opal.