Unique Lightning Ridge Black Opal Minerals 2:21 PM A+ A- Print Email Photo by Wood's Stoneworks and Photo Factory on Flickr Opal | #Geology Formula: SiO₂·nH₂OColour: Colorless, white, various Hardness: 5½ - 6½Lightning Ridge Black Opal it is like lightning bolts that flash and change as it moves. Australia. Types of opal with photos