Description and pricing information about Opals from Lightning Ridge Australia :
LIGHTNING RIDGE OPALS
How to evaluate opals
You can evaluate opals with a system of points, which take into consideration the Body tone , Colours , Brillance , Pattern , All lights and Shape, and then multiplied by the amount of carats.
A black body tone is usually the most expensive ! The brilliance is also a major factor when pricing an Opal.
But it all comes down to personal taste and what someone is willing to pay for that very special piece.
Even Opals with inclusions can be priced very high because there is a certain uniqueness to it.