A doublet is a type of opal composed in two sections. It is sometimes used to imitate other, more opals.An opal doublet uses a thin slice of opal for the top portion of the stone.natural opal is fused to a black stone backing. The color of the opal used in the doublet is all that is seen...If seen in reflected light, a separation line may be seen. In the case of opal doublets, a backing layer of onyx or matrix (ironstone) gives the more fragile opal layer support and can make the opal look darker and higher quality Source your doublet opals direct from opal miners and opal wholesalers and dealers for your single gem doublet opal or parcel doublet opals from Australia Black doublet opals are made in lightning ridge using opal crystal and set on natural black opal potch. most doublets are set on natural ironstone from Queensland opal fields