Reference:

ABOUT OPALS

What is an Opal Triplet ?

Composite natural opal consists of natural opal laminates, manually cemented or attached to another material. The opal component is natural opal. TRIPLET OPALS – are a composition of three pieces where a thin slice of natural opal cemented between a dark base material and a transparent top layer (usually of quartz or glass).
Mosaic and Chip Opals – are a composition of small flat or irregularly shaped pieces of natural opal cemented as a mosaic tile on a dark base material (Fig. 14) or encompassed in a resin.

	Fig. 14. A mosaic dark opal composite. (Photograph, R. Weber)

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.

Triplet

Thin slice of precious crystal opal glued between crystal cap on top and black backing

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