Opal
 
 
October Birthstone.   14th Anniversary Gemstone; and , 34th Anniversary Modern Gift.
 
A Mysterious World of Color
 
It is no wonder why early cultures from around the world have attributed magical properties to the Opal.   The mysterious patches of color that appear and disappear with every movement give Opals a life of their own.  Opals have been collected for thousands of years.   Estimated to have been collected at around 4000 B.C., the oldest Opal artifact was found in a cave in Kenya.   Opals were one of the most highly prized gemstones to the Greeks and Romans.   Early Greeks believed Opals were the source of prophetic powers.   As the Roman Empire grew, so did the demand for Opals.   A Roman Senator, Nonius, chose to be exiled rather than give his valuable Opal to Marc Antony who wanted to give it to his lover, Cleopatra.   A legend tells of a Roman Emperor who offered to trade one-third of his kingdom for a single Opal.   The Roman natural historian expressed his difficulty in describing the gem: "... it is made up of the glories of the most precious stones.   To describe it is a matter of inexpressive difficulty: There is in it the gentler fire of the Ruby, the brilliant purple of the Amethyst, the sea-green of the Emerald, all shining together in an incredible union."   These fiery stones have often found their way into the jewelry and crowns of royalty.  Queen Victoria adored Opals and kept a fine collection.
 
While Opals have always been an object of curiosity and mystery, the powers attributed to it have not always been positive.   In the late 18th century, the Opal was considered to bring bad luck to its possessor.   The Spanish King Alfonso XII had given an Opal ring to his wife who died shortly thereafter.   The ring was passed on to family members and each person who wore it died mysteriously.   Eventually, the king himself wore the ring and he too died unexpectedly.   While historians will say that the deaths can be attributed to the cholera epidemic of the times, many have blamed the deaths on the Opal.
 
Where are Opals Found?
 
Common Opal is Common - Precious Opal is Precious
 
Opals are found on every continent and in nearly every country.   Some pieces are hundreds of pounds, but the vast majority of it is what we term common Opal, that is Opal without any fire.   And, even of the small portion of Opal that does have fire, most of it is unstable.   Some examples of places that produce this kind of Opal are:  Rainbow Ridge, California; Virgin Valley, Nevada; or Spencer, Idaho.   Opal has to be both stable and have nice fire to be considered precious Opal.   Only a very small portion of naturally occurring Opal can be considered gem-quality, and ninety percent of it comes from Australia.   Some of the Australian Opal fields are Andamooka, Mintabie, Queensland, and White Cliffs, but two of the more important Opal-producing areas in Australia are the Coober Pedy and the Lightning Ridge mining areas.
 
Australia is the Largest Producer of Opals in the World
 
Coober Pedy Opals
 
Opals were first discovered in Coober Pedy in 1915 A.D.   Since then, this Australian mining area has produced the majority of gem-quality Opals.   The Coober Pedy mining area produces far more Opal than Lightning Ridge.   If you were to walk into 50 jewelry stores, it is likely that you will see only Coober Pedy Opals.   This mining area sits on an ancient sea bed.   As a result, there are many fossils in this area.   Fossilized Opals are formed when silica gel seeps into a gap left by a sea creature.   The result is an Opal in the shape of a shell, fish, or some other ancient animal.   Fossilized Opals are commonly found in Coober Pedy.
 
 
 Lightning Ridge Opals
 
Lightning Ridge is a famous name in the world of Opals.   The name of the area originated from an episode of bad luck when a shepherd, his dog, and 600 sheep were killed when lightning struck them while finding shelter on one of the ridges.   Their bad luck gave way to an abundance of good luck beginning with the discovery of Opals in the Lightning Ridge area in 1873 A.D.   Since then, the Lightning Ridge mining area has produced some of the finest Opals in the world.   This mine does not yield as many Opals as the Coober Pedy mining district, but the quality of Lightning Ridge Opals is superior.   The most valuable Opals are the highly prized black Opals from Lightning Ridge, and roughly 99% of all Black Opals come from this mine.   Opals found in this mining district have broad patches of bright fire.   Sometimes the fire is so bright, it seems almost electric.   One of the more unique qualities of these Opals is that their fire stays bright, even in low light.   This kind of fire is rarely seen in the stones from other mines.   Fossilized Opals are also found in Lightning Ridge, but they are usually in the shape of organic material like trees and plants rather than sea animals.
 
Classifying Opals
 
There are three main factors in the description of an Opal:  Base color, Transparency, and Type.   The color of an Opal can be a point of confusion, since most Opals display several different colors.  There are two color characteristics in Opals; the background color and the color associated with the fire.  It is the background color that is being referred to when an Opal is described as a black Opal or a white Opal.  If you ignore the fire in a black Opal, the background color is black.   Due to its complex non-crystalline composition, Opals interact with their environment in a variety of ways to create a variety of background colors.   The color can originate from a substance that is naturally associated with the Opal or it may originate from the Opal itself.   Opal with fire can occur in a variety of background colors.   Australia produces a lot of white and semi-clear material and is most famous for its black Opals.
 
When an Opal is described as “crystal” or “semi-crystal”, it is the transparency that is being described.  This terminology can be confusing because Opals do not have a crystalline composition.   A “crystal” Opal is an Opal that is transparent (no base color).  A “semi-crystal” Opal is an Opal that is semi-transparent (translucent).
 
What Determines an Opals Value?
 
Generally, boulder, matrix, assembled (doublets, triplets), man-made, and imitation Opals are much less valuable than natural solid precious Opal.  Below are some factors that influence the price of natural precious Opals.
 
Blind Angles:   When an Opal is rotated, if the color disappears at any angle, that angle is a blind angle.   Many blind angles will depreciate the value of the Opal no matter how bright the fire is from one particular angle.   The worst blind angle is when the viewer is looking directly at the front of the Opal.
 
Blind Spots:   When an Opal is stationary, the areas of the opal not displaying colors are blind spots.   An Opal with a smaller percentage of blind spots will generally be more valuable than one with a larger percentage.   A valuable Opal will have fire that covers most of the Opal from all angles.
 
Brightness of Fire:   The value of an Opal goes up as the brightness of its fire increases.
 
Color Range:   The kind of color the Opal displays affects its value.   Opals that display red fire are the most valuable.   Opals that display blue-green fire are less valuable than those with red fire.   Opals that only display blue fire are least valuable.
 
Fire Pattern:   Opals with larger flakes of fire are more desirable than Opals with smaller flakes.
 
Cutting Quality:   Thicker Opals will carry a premium because of increased durability.   Regular shaped Opals (oval) are more valuable than irregular shaped Opals.
 
Background Color:   White Opals are the most common Opals and typically less valuable than the rarer black Opals.   Black Opals are the most sought after color.
 
How Should I Care for My Opal Jewelry?
 
CAUTION:   Opals are not as hard, nor as tough, as other gemstones, so they can more easily be damaged.   Never subject Opals to extreme temperatures (eg. boiling water, freezer).   Thermal shock can weaken or break your Opal.   If you wear your Opal jewelry, it is unlikely that you will subject your Opal to temperatures that will cause it to crack.   Over time, an Opal set in a ring will get scratched from normal wear and will need to be repolished.
 
 
Formation of Opals
 
Opals are chemically similar to Quartz, Amethyst, and glass.   However, unlike most gemstones, Opals are not composed of crystals.   Their makeup is primarily silica and water.   Opals are created when weathered silica seeps into fissures as gel.   At this point, the silica gel contains a large amount of water and would flow just like a glacier.   You can see what opals would look like during this early period of formation by mixing sodium silicate (more commonly known as “Water Glass” in pharmacies) with vinegar.   As the water evaporates, the gel hardens.   How quickly the water evaporates determines stability of the Opal.  If the water evaporates slowly, the Opal will be stable, and if it has nice fire, it will be considered gem quality.   Gem quality Opals usually contain less than 10% water.   If an Opal has a small concentration of water, an evaporation event capable of causing instability fractures) is less likely to occur.
 
The Cause of Color in Opals
 
A common myth is that the fire is caused by the water contained within the Opal.   The misconception is that the colors are caused by diffraction, just like a rainbow.   This is not true.   Opals are composed of tiny silica spheres.   When the spheres are the same size and are arranged in a three-dimensional grid, negatively charged areas are created in the gaps between the spheres.   If those negatively charged areas are as big as a wavelength of visible light, then colors will be visible.   One reason Opals with red fire are so popular is because an Opal with red fire will also display every other color.   Red light has the largest wavelength followed by orange, yellow, green, blue, and violet.   If an Opal displays red fire, then that means the negative areas between the spheres are as big as the largest wavelength of visible light.   As the Opal rotates slightly, the colors change as the negative areas become gradually smaller from the viewer’s perspective.
 
A Gem of a Beetle
A researcher has discovered that a beetle, Pachyrhynchus argus, has scales that emulate the structure of Opals.   The effect of the scales' structure is that the beetle displays a metallic green color for the same reason that Opals display fire.   Scientists are trying to discover how this beetle creates this structure so that they can learn to emulate it.  Success would be a technological breakthrough in the synthesis of Opals.   Opals have many industrial uses.  Currently, there is research being done on chemical detection using synthetic Opals.   This beetle could potentially save lives in the future when synthetic Opals are employed to detect dangerous chemicals in a terrorist attack.
 
 
 
 
 
 
GB Jewelers, Inc.
Under the Clock Tower
675 SE Marlin Avenue, Suite 1  /  PO Box 999
Warrenton, OR 97146
800-869-1481

Latitude:  46.159033 / Longitude: -123.9055280
 
 
Store Hours: 10:00 a.m. - 6:00 p.m.
Monday - Saturday
 
Copyright 1974