What is an Australian opal doublet ?

An Australian opal doublet is a layer of light precious and natural Australian opal attached to a background made of black potch ( black opal without fire) or nowadays boulder from Queensland.
The opal used is an opal from Coober Pedy, in the State of South Australia.
It is an opal composite.
It costs a lot less than a solid opal and can last many years without deteriorating.
It is sensitive to water. Do not get it wet or immerse in water.