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Wednesday, August 11, 2010

GEMSTONE JEWELRY - common gemstones !

Agates, Jaspers and Obsidians are found world-wide. They come in so many varities, colors and consistencies that it takes many books to try and identify the various types. Because of their commonality world-wide, names can also be confusing as many are named for local places or people or designs within the stones, and thus do not carry a common name world-wide.
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This design encorporates a black Druzy Agate off-center heart shaped wire-wrapped pendant hanging on a necklace constructed of black Agate (Onyx) hearts and snowflake Obsidian beads with silver highlights. Matching French Hook hoop earrings complete the set.
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Druzy is the term that refers to a blanket of tiny, sparkling crystals often found inside a geode of Quartz or an Agate. The sparkling appearance of druzy is like that of spilled salt or sugar. The formation of the tiny crystals occurs after molten rock begins to quickly cool, trapping gasses within it as it solidifies. The trapped gasses cause crevices and cavities in the cooling rock. Nutrient-rich groundwater later flows through these gaps and crevices, depositing layer after layer of minerals which crystallize on top of each other. The resulting encrustation is called druzy (drusy, druse, druses). This process doesn't take days or weeks, but a few hundred or even a few thousand years.
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Jewelers use the term Druzy for all gemstones with the crystalline structure referred to above. Golden druzy is often of Quartz, but other colored druzy gemstones were made in nature by the depositing of different minerals, which give them their unique colors of blue, pink, lemon yellow, turquoise or blue. Jewelry labeled "golden druzy," has actually been put through a special process to create the golden look. A shiny golden druzy gets it glitzy looks thanks to a process known as 'vapor-coating' or 'vapor-deposition'. '''Vapor-coating begins in a vacuum chamber. The high-karat gold (or platinum, titanium, silver or copper) is converted to a vapor and then mixed with oxygen. The gold-oxygen vapor settles on the crystals of the druzy and bonds with them at the molecular level. Other minerals have also been used to give blue, red and green colorations. So when obtaining a Druzy, be sure to ask if natural or vapor treated.
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Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools rapidly without crystal growth. Obsidian is commonly found within the margins of Rhyolitic lava flows known as Obsidian flows, where the chemical composition (high silica content) induces a high viscosity and polymerization degree of the lava. The inhibition of atomic diffusion through this highly viscous and polymerized lava explains the lack of crystal growth. Because of this lack of crystal structure, obsidian blade edges can reach almost molecular thinness, leading to its ancient use as projectile points and blades, and its modern use as surgical scalpel blades. In some stones, the inclusion of small, white, radially clustered crystals of Cristobalite in the black glass produce a blotchy or snowflake pattern (Snowflake Obsidian). It may contain patterns of gas bubbles remaining from the lava flow, aligned along layers created as the molten rock was flowing before being cooled.
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Black Agate (Onyx) which is truely a died black Agate, is more common and perhaps the most famous variety, but not as common as natural Onyx. Onyx is a crypyocrystalline form of Quartz. The colors of its bands range from white to almost every color (save some shades, such as purple or blue). Specimens of Onyx contain bands of colors of white, tan, and brown. As stated, the pure black form which most people know as Onyx, is not a naturally occuring variety. Black Agate or poorly colored Onyx is heated and dyed black to come up with the pure black form so well liked within the jewelry industry.
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