Black Opal is most valuable type, coming mainly from lighting Ridge. High quality stones are very rare and magnificent body colour. Light Opal is mostly mined at Coober Pedy and Mintabie (SA), although the first deposits were found at white Cliffs (NSW).
Stones range from being transparent to nearly opaque and have a light or white body tone or background hue. Crystal Opal includes light or black opal which is transparent or very translucent. Colour can be seen from deep within the opal.
Boulder Opal occurs naturally in hard rock mined predominantly in Queensland. It is easily identified because, when cut, the host rock (a brown ironstone) is left on the back of the opal.
Double Opal is a composition of two pieces where a slice of natural opal is cemented to a darkened base material to enhance colour.
Triplet Opal is a composition of three pieces where a thin slice of natural opal is cemented between a dark base material and a transparent top layer (usually of glass or quartz)