Reference:

ABOUT OPALS

What is an Opal Doublet ?

Composite natural opal consists of natural opal laminates, manually cemented or attached to another material. The opal component is natural opal. There are three main forms of composite opal:  
Doublet Opals – are a composition of two pieces where a slice of natural opal is cemented to a base material (Fig. 13).

	Fig. 13. A ring-mounted black Lightning Ridge-type composite doublet opal. (Photograph, G. Brown)

In addition to solid opal, a number of other varieties composite opal are widely available, as outlined in Table 2 below. Composite stone are generally more affordable than solid stones as smaller amounts of precious opal are used. In all cases, thin slices of opal are glued to a backing of black backing material.

Doublet

Thin slice of precious crystal opal glued to black backing material . When the backing is brown ironstone it is often called a boulder doublet

Any opal field producing crystal opal

Find more information at the OPAL Association's Opal Nomenclature Section of their Website:

http://www.opal.asn.au/information_nom