Classified by the Opal industry as Natural Opal Type 1 A Dark Opal is defined when the Opal is presented in one piece in its natural state apart from cutting or polishing, and is of substantially homogenous chemical composition. Genuine Natural Australian Dark Opal is known as the lucky gem from the lucky country . A hydrated amorphous form of silica SiO2A��ˌ?nH2O consisting of spheres of silicon dioxide molecules arranged in regular, closely packed planes. And often found in Lightning Ridge, Australia. Guaranteed free of dyes and artificial colour. With Base tones ranging from Black (N1-N4) Black Opals with evidence of Iron Oxide and mined from Lightning Ridge that have a base body tone of (N5-N6) are today defined as Dark Opals ��ˌ? (which in the past have sometimes been referred to as Grey, dark or Semi-Black ��ˌ?) and have been mined in fields such as Mintibie and found in limited quantities in various Other Opal mining fields.