Colorless, white, yellow, orange, red, green, blue, brown, gray & black
Australia, Brazil, Mexico, Honduras, Czechoslovakia & Nevada
Opals with play of color are cut into cabochons. Fire Opals without play of color are faceted
With "the fire of the carbuncle, the brilliant purple of the Amethyst and the sea green color of the Emerald, all shining together in incredible union" Opal clearly impressed Pliny the Elder (23-79 AD), Roman historian and author of the world's first encyclopedia. The Romans considered Opals a symbol of hope and purity while for the early Greeks they embodied the powers of foresight and prophecy. The more fancifully minded Arabs thought that Opals must have fallen from heaven in flashes of lightning thus achieving their unique play of color or "Opalescence".
Amazingly this Opalescence is a result of the 5-10% of water trapped inside the stone, in which rows and rows of tiny spheres of silicon dioxide are arranged, diffracting light in a unique fashion.
The physical structure of Opal is unique. Tiny spheres of silicon dioxide form a pyramid shaped grid interspersed with water. Tiny natural faults in this grid cause the characteristic "play of color". The effect is similar to the rainbow colors displayed on a soap bubble, only much more dramatic.
Opals vary widely in body color, with white the most common. Black is considered the most valuable as it enhances and accentuates the play of color. Fire Opal (yellow, orange or red) is often faceted and can resemble Ruby. Green and Blue Opals are rare.
As Opal is relatively soft and fragile it is often made into doublets or triplets - backed with plain black Opal and fronted with clear quartz. These are ideal for rings or any piece that is likely to be receiving rough treatment.
Combining body color and play of color we are faced with infinite possibilities, so pricing is complex. Size is also a factor with the carat price for larger stones accelerating accordingly. The intensity of the play of color and the extent to which it covers the Opal's surface also count.