Black opal is found only in Australia in Lightning Ridge, the most famous opal deposit in the world since it was discovered in 1903, and in Mintubie, which also produces large quantities of light opal. Another large opal producing area in Australia is Coober Pedy, which produces light opal. This type of dwelling is quite practical and cool as temperatures soar in the daytime. Another more unusual type of opal is boulder opal, which has opal with an ironstone host rock matrix which creates a natural dark background to view its fire. These are particularly favored for earrings, since they are mirror images of each other.
Boulder opal is produced in several areas in western Queensland.
Crystal opal, the next most costly type of opal, is transparent with flashes and is highly valued due to the brilliance of its colors and the fact that many layers of color within the stone can also be seen. White and milky opals tend to have more diffused colors due to the light background color. This is the most affordable type of opal. Andamooka is known for producing crystal opal and light opal. Within each opal variety, the brillance of the play of color is the most important value factor.