Gemstone Glossary

Opal
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 had been wearing opals for centuries and considered them 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. Opal has also featured in literature with Shakespeare referring to it in Twelfth Night as "the queen of gems". Meanwhile, Queen Victoria had to intervene in the near destruction of the 19th century opal market when the writer Sir Walter Scott started a superstition that opals were bad luck for people not born in October. In this novel the heroine owned an opal that burned fiery red when she was angry and turned ashen gray upon her death. Queen Victoria finally dispelled the curse by giving opal jewelry as gifts at a royal wedding.

Opal and tourmaline are the official stones for those born in October, and famous French actress Sarah Bernhardt rarely left the house unless adorned with her opalescent birthstone.

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.

Opal is sometimes cut with pieces of matrix - the host rock. This strengthens the opal and can also lend a more interesting appearance. The finest examples are Boulder Opal, which sometimes have an undulating surface of "hills" and "valleys". Their unusual shapes and ironstone inclusions make Boulders popular with progressive, modern designers and wearers and are most popular as Opal brooches. Opal pendants, Opal necklaces and Opal earrings are also gaining in popularity.

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 opal 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.

Of all the opal taken out of the ground, 95% is valueless "potch" and 95% of the remainder is low quality. Only a mere 0.25% ever makes it to market.