PRECIOUS OPAL

Precious Opal, the October Birthstone, has been highly prized for many centuries. From the Roman times, when only emerald was considered more desirable by the Romans, Precious Opal has been used as human adornment. Opal is an inorganic mineral, unlike Quartz it’s close cousin, Opal is not crystalline, it is considered a hardened jelly with the formula SiO₂n H₂O, silica with chemically combined water. It varies from 1-21% but about 6-10% is normal in the Precious Opal. There are four major classifications of Opal used to make jewelry. White, Black, Fire and Water Opal are the four different types used.

White Opal is the most common type of opal used in jewelry. It is found in abundance and is inexpensive. Black Opal has a black or dark blue, green or grey body color and exhibits vivid flashes of color from the dark body. Fire Opal is a translucent stone with a orange-red to red body color and may or may not show “Play of Color”. Finally water Opal shows flashes of color in a clear colorless stone.

During the 18^th and 19^th century Opal got a bad rap for being bad luck. This probably was based on Teutonic Superstition at the time. Also may have come from a popular novel of the time by Sir Walter Scott, “Anne of Geierstein”, in which Opal played a malevolent role. Of course this is based purely on fantasy and not fact. I believe anyone lucky enough to own an Opal knows that it is a blessing and not a curse.

The actual cause of the brilliant flashes of color in Opal is due to its structure. There were many theories bandied about that tried to explain how those flashes happened, however with the invention of the electron microscope around 1964 it was discovered that the structures in opal that created those wonderful colors were made up of millions of microscopic uniform spheres of amorphous silica regularly stacked with arranged “voids” in between. The size of the spheres decides the color in the stone. This play of color in Opal is an iridescent effect and not “opalescence” as sometime described.

Opal is a petrifying agent and is considered pseudomorphous after wood. That is why you may see opalized petrified wood or other opalized fossils and minerals. The most interesting psuedomorphs in Opal are the opalized fresh water and marine shells and bones of prehistoric animals. Opal is more common than you might suspect, it just doesn’t always show a “play of color”. It also may occur in seams in layers of sandstone in many parts of the world.

Australian opal is the most famous of the precious opals and is prized above most. White Cliffs, Andamooka, Cooper Peddy and Lighting Ridge are synonymous with Australian Opal. In reality fine opal is found in places like Jalisco Mexico, Humbolt County Nevada, Honduras, Brazil, Guatamala, Mexico and even Czechoslovakia where it is assumed the Romans got their Opal.

Occurances and varieties of Opal are a book in itself. The chemistry and physics involved in understanding the amazing light refraction of Opal is pretty involved, Opal is one of those special gems that at first defies the imagination as to how it can produce such vibrant and vivid colors. As I’ve learned there is no end to the variations of opal and it’s colors. Many people have made a lifetime study of this Gem Material and still after all the centuries it can still keeps us mesmerized. So leave it to say just have a look for yourself, it is a true wonder of nature.