BE THE OPAL AMIDST THE DIAMONDS
HAPPY BIRTHDAY TO OUR OCTOBER SUMMIT FRIENDS
Like several of the world’s most popular gems, opals are believed to have originated in India. In Sanskrit, opals were called “upala,” meaning “precious stone.” When these ethereal gems were brought to the Western world, ancient Romans called them “opalus.” Bedouin tribes used to believe that opals contained lightning that fell during storms, and Ancient Greeks thought these stones gave the gifts of prophesy and health. In the past, opals were also believed to symbolize purity and hope due to their celestial coloring. Because of their unique smooth but fiery look, opals are most often polished in the cabochon style — a style where a gem is shaped and polished instead of faceted. In addition to being the birthstone for October, opals are also the traditional 14th wedding anniversary gift.
Opals are popularly known for their milky, rainbow-colored glow and fire. While white opals are the most common and popular, opals have hues ranging across the whole color spectrum including black opals, pearlescent pinks, pale greens, and more. Opals are beloved for the dramatic “play of color” that shimmers in bursts throughout the stone.
DID YOU KNOW?
In Australia, precious opal is found in Cretaceous age sandstones and mudstones. These sedimentary rocks were deeply weathered and this weathering released silica into the groundwater. Small faults and joints in the rocks formed pathways for movement of the groundwater as it penetrated downwards.
Impermeable barriers between the sandstone and the underlying rocks trapped the silica-carrying groundwater where it slowly hardened into a gel forming opal in veins and lenses.
Opals are frequently layered and if a rare red layer is present it is at the base in the thinnest portion of the vein and indicates that gravity played a part in the arrangement of the silica spheres.
Australia is the only part of the world where opalised animal and plant fossils have been found. At Lightning Ridge in NSW, small opalised dinosaurs and primitive early mammalian remains, together with shallow marine shellfish and crustaceans have been found. Probably the most famous opalised fossil is Eric the Pliosaur (Cretaceous age marine vertebrate) which was found at Coober Pedy and now forms part of the Australian Museum collection. Not only is the opalised skeleton of this animal preserved, but also the stomach contents of its last fish meal are replaced with opal. Opalised fish bones and shelly mollusks are also fairly common at Coober Pedy, SA and are valued according to the appearance of the individual specimen and the intensity of the play of colors.
Spectacular mineral replacement with opal can also occur. The so called ‘opal pineapples’ found at White Cliffs, NSW are opal pseudomorphs of the mineral ikaite. Queensland opal deposits occur in non-marine sedimentary rocks and opalised animal remains are very rare, however fossil wood fragments showing annual growth rings and cellular wood textures occur and sometimes these are beautifully replaced with precious opal.
Australian black opals are the rarest type of opal ever found and can fetch the highest price per carat than any other opal in the world. What makes a black opal so rare is the phenomenon of dark to black underlying body tone or potch, which helps to intensify the brightness of the color bar. On the body tone scale, black opal will sit between N1 to N4.
The body tone is gauged by the face or top of the gem and should not be confused with play of color. The body tone of an opal should never be determined by the back of the gem. However, the potch in a black opal usually found on the back of the gem can help the overall body tone to become darker, as long as the potch sits directly behind the color bar naturally helping the play of color to become darker.
Black Potch is the main reason why black opal is so rare. Potch, also known as common opal, which is opal silica, has no real value unless there is play of color. Most opal fields produce common potch but black potch is predominantly found in Lightning Ridge with gem play of color.
Boulder opal is a unique type of opal that is only found in Queensland and is one of the most sought after types of Australian opals.
Boulder opal has an attribute like no other due to its formation in an ironstone host rock, found in brown ironstone boulders. The opal is usually formed in thin veins through the ironstone and has to be opened or split to find the face of color. The face of the boulder opal is mostly undulating because it follows the natural seam in the boulder. Often we refer to a pair of opals with the same pattern as a boulder split because it has been split down the middle of the vein of color creating two faces with the same pattern and color.
Fire opal is mined in the Mexican states of Queretaro, Hidalgo, Guerrero, Michoacan, Julisio, Chihuahua and San Luis Potosi. The most significant deposits were discovered in Queretaro in 1835, and are still producing today. Small quantities of this gem can also be found in Oregon and British Columbia.
The name tourmaline comes from the Sinhalese word “toramalli,” meaning “stone with mixed colors.” This is because many tourmaline gems feature multiple colors in one crystal formation, and some can also appear to be different shades when looked at from different angles. One of the most famous examples of this is the “watermelon” tourmaline that features red and green stripes. In fact, there are very few types of gems that offer such a variety of colors as tourmalines do. According to ancient Egyptian legend, the stone traveled along a rainbow collecting all of the rainbow’s colors, which is why tourmaline is found in such a multitude of hues. Some of the most popular tourmaline colors are emerald green, red rubellites, and October’s birthstone of pink tourmaline. Because of its all-encompassing color variety, it’s believed that tourmalines help inspire art and creative expression.
Also because of its range of colors, tourmalines have often been mistaken for other gemstones throughout history. Conquistadors from Spain found green tourmalines in Brazil in the 1500s and mistook the gems for emeralds. One of the “rubies” in Russia’s “Caesar’s Ruby” pendant – part of the Russian crown jewels – is actually a red rubellite tourmaline. It wasn’t until scientists recognized tourmalines as a unique mineral species in the 1800s that these and several other famous gems were recategorized as tourmaline.
Different tourmaline colors are believed to have different healing properties or powers.
Tourmaline is famous for its dazzling colors. There are rich reds, pastel pinks, peach colors, strong greens, bright yellows, and deep blues. Some have more than one color, like watermelon, which is pink in the middle and green around the outside. People confused tourmaline with other gems, like emeralds and rubies, until the 1800s. That’s when scientists recognized tourmaline as a unique mineral.
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