Opal Stone Value
Black Opal - Tone N1 to N4
Dark Opal - Tone N5 to N6
Light Opal - Tone N7 to N9
Crystal Opal
Boulder and Matrix Opal
Composite Opals
Doublets prices are usually 15% to 35% of the value of similar looking natural, (solid,) gem. However, they occasionally run as high as 50% of a natural opal if they are of exceptional quality. Triplets are only about 1% of the value of an equivalent natural and peak at $500.
Other Opal Types
Contra Luz
Fire Opals - Faceted
Fire Opals - Cabochons
Pink Opal
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
Evaluating precious opal is a highly refined art. For details, see our articles on Appraising Opals and our Opal Buying Guide.

78 opal cabochons from Welo, Ethiopia (52 ctw) in 18k gold bracelet. © Rob Lavinsky, www.iRocks.com. Used with permission.