Opal Facts

Appearance

• Precious opal interacts with light to create sparks or flashes of the colors blue, green, yellow, orange and red, plus aqua and purple, occasionally. Not all opals show all these colors. Blue flashes are most common, then blue occurring with green, then blue occurring with green and yellow, then those plus orange, with red flashes the most uncommon. An opal displaying red can show the other colors as well. The background of an opal---the body color---can be milky (white opal), clear (water opal), brown or gray or black. Black opals command the highest prices.

Formation

• Opals are formed in the cavities of rock, usually sedimentary rock, which is formed when sediment is laid down, buried and pressed to make rock. Silica is carried by water into the cavities, and when the water evaporates is left behind. Silica that collects into spheres of uniform size and distribution---that is, they are packed together efficiently---creates precious opal. Sometimes fossils become opalised---that is, an opal that is forming takes the place of a bone, shell, teeth or other organic matter, preserving a record of the object as it decomposes away.

Play of Color

• Spheres packed together leave gaps. When light passes into an opal, it bounces around through the silica spheres and the gaps among them. It bends as it enters some of the material. It also is diffracted, the white light split into rainbow colors. When the light comes back out of the opal, you see the colors the opal and light have created. The smallest spheres produce the blue colors, while the largest ones produce red. Since this play of color is so unusual, the term opalescence, to describe such iridescence, was coined.

Types

• Besides precious opals, there are also opals that do not possess the play of light. These opals are called common opals, also known as potch. Common opals are less valuable than precious opals, but can be cut and polished to make jewelry. The potch is sometimes adhered to the bottom of opals before using it in jewelry. Among the precious opals, body color gives us four basic types: white opals, black opals, fire opals and crystal or water opals. White opal, also known as light opal, is the most common of the basic types, with a body color of white, yellow or cream. The body color of a black opal or dark opal is black or dark gray. Sometimes, opals with a body color of dark blue or green are also called black opals. Fire opals are transparent or translucent, with no color play. Instead the stone has color throughout. Crystal opals are also transparent, but do have the play of color. Another type of opal is the boulder opal, which has a layer of stone from mining left on opal that occurs in a thin layer. These boulder opals can command prices second only to black opals.

Composite Stones

• Usually, opals used in jewelry are one piece of solid opal. Some opal, though, is found in very thin layers. When that happens, the opal is sometimes glued to a base, often potch, but also obsidian or basalt. This product is called an opal doublet. Since opals are about the hardness of glass, to protect the opal layer of the doublet, sometimes a transparent top is placed over it, often of quartz. This product is called an opal triplet. Composite stones should not be soaked in water, otherwise the glue can dissolve.

Popular Positive Reputation

• In most cultures and throughout history, the opal is and has been believed to be a lucky stone imbued with mystical or supernatural powers. Among Europeans, opal is a symbol of hope, truth and purity. Ancient Romans and Greeks believed opals kept the wearer safe from disease. The Greeks believed also that opals imbued a gift of prophecy. Opals are also believed to enhance inner beauty, inner vision and eyesight, help the wearer recall past lives and see the great possibilities available. Arabs believed that opals fell from heaven in lightning flashes. Australian aborigines have a large body of beliefs regarding the opal, and feel the stone has a spiritual value. They believe the opal is a remembrance of an ancestor. Aboriginal mythology holds that fire was given through the opal. In the East, the opal is thought of as the anchor of hope.

Popular Negative Reputation

• Negative connotations have attached themselves to the opal, some because of the opal's reputation for supernatural powers, some from rumor meant to decrease its value and some from misunderstanding. Opal's appearance can sometimes look a bit like a cat's eye, or take the shape and color of other creatures' eyes. Superstition regarding witchcraft was then transferred to the stones. One negative belief is that opals are bad luck to any but the wearer. This belief stems from "Anne of Geierstein," a novel by Sir Walter Scott, some readers drawing the bad-luck conclusion from their reading. Some diamond dealers of the past sought to slow the popularity of opals, once they became more available after their discovery in Australia, resurrecting some of the negative beliefs about opals.