DO YOU KNOW HOW OPAL IS VALUED? Opal is a precious gem, the best of which can challenge diamonds in price per carat. As the prices paid for Opal vary so greatly, a basic understanding of the factors influencing the VALUE of opal will ensure a well informed purchase. BACKGROUND COLOUR - Black opal is more valuable than a clear opal (crystal) which in turn is generally more valuable than a white or milky opal. DOMINANT COLOUR - A stone with strong COLOUR and a full spectrum range is generally more valuable than one with a predominant red fire, which is more valuable than one with predominantly green COLOUR which in turn is more valuable than a stone showing only blue COLOUR COLOUR PATTERN - 'Harlequin' opal, where the COLOUR occurs in regular patches is more valuable than 'Pinfire' where the COLOUR is in small specks. WEIGHT OF TIE STONE - Solid stones are sold by carat weight (20 mg per carat). Dividing the cost of the stone by its carat weight will provide you with a guide to the stone's overall value.