The valuation of opal is a complex subject and would require
an entire book to describe it in detail.
If you are interested to spend some time then there is an
excellent book which covers opal valuation quite thoroughly: Opal Identification
& Value by Paul B. Downing, 2003,
Majestic Press, Inc.
As an alternative there is a software named
Smart Chart" available on CD which takes you through the entire valuation
process, step by step. You only have to select the opal's characteristics (e.g.
Brightness, Body Tone, Transparency, Colour, Pattern, Weight etc.) after which
the program calculates the appropriate wholesale price per carat.
Soon we will provide here a short table which gives you an
idea of the approximate retail value of an opal in relation to its most