Black Opal is the most valuable and sought after opal and derives it's name from the background color or the color of the back of the opal. Black opal contains carbon and iron oxide trace elements, which give it the dark appearance and
The darker, or more black the background the more valuable to stone may be.
Crystal opal is translucent when held up to the light and is found at Lightning Ridge and Coober Pedy in SA.
Comes from ironstone and is mined in Queensland.
Found at Coober Pedy in South Australia. White Opal also produces crystal opal.