Opal Variety	Example	Identifying features and rareity	Area of Origin
Light Opal		White or light appearance. Most abundant and affordable	Usually South Australian fields though some from other areas
Crystal Opal		Transluscent appearance - a printed page would be roughly visible through the stone. Relatively abundant.	Most opal fields
Boulder Opal		Usually thin layer of precious opal naturally adhering to brown ironstone host rock. Relatively abundant	Queensland opal fields
Andamooka Matrix Opal		Black or darkish bodied opal with bright specs of colour. This is chemically treated Limestone matrix with precious opal in voids. Not common	Andamooka South Australia opal field
Dark Opal		Precious opal with a grey or darkish appearance when viewed from the front. Dark opal is relatively abundant	Usually Lightning Ridge area in NSW or Mintabie in South Australia
Black Opal		Precious opal that has a black appearance when viewed from the front. Only opal that looks as dark as the N1-N4 body tone scale (below) can be truly called a black opal.Rarer than light or dark opal	Usually Lightning Ridge area in NSW or more rarely Mintabie in South Australia

Table 1: Types of Solid Natural Opal

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.

Opal variety	Example	Distinguishing features	Area of Origin
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
Triplet		Thin slice of precious crystal opal glued between crystal cap on top and black backing	Any opal field producing crystal opal
Mosiac		Thin chips of precious crystal opal glued onto black backing, can be used in doublets, triplets or on watch faces.	Any opal field producing crystal opal
Inlay		Small thin pieces of precious crystal opal glued directly into channels in jewellery	Any opal field producing crystal opal

Table 2: Types of Composite Opal

While most composite stones are made from natural opal, occasionally synthetic opal is used in doublets or triplets. Consumers should ask the supplier to confirm whether opal used in composite stones is natural. Also note that whilst composite stones generally have the appearance of black opal, none can be correctly described as black opal.