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Gemstones are basically categorized based on their crystal structure, specific gravity, refractive index, and other optical properties, such as pleochroism. The physical property of "hardness" is defined by the irregular Mohs scale of mineral hardness. Gemologists study these factors while valuing or appraising cut and polished gemstones.
Cutting and polishing diamonds in the Netherlands, 1946. The art of cutting a gem is an exacting procedure performed on a faceting machine.The ideal product of facet cutting is a gemstone that displays a pleasing balance of internal reflections of light known as brilliance, strong and colorful dispersion which is commonly referred to as "fire", and brightly colored flashes of reflected light ...
In Australia, there are numerous gem shows, including an annual gem show called the GEMBOREE, which is a nationwide lapidary competition. There is a collection of gem and mineral shows held in Tucson, Arizona, at the beginning of February each year. The event began with the Tucson Gem and Mineral Society Show and has now grown to include dozens ...
Group of precious and semiprecious stones—both uncut and faceted—including (clockwise from top left) diamond, uncut synthetic sapphire, ruby, uncut emerald, and amethyst crystal cluster. A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or polished, is ...
This is a list of gemstones, organized by species and types. Minerals ... Rock crystal (var.) Shocked quartz (var.) Smoky quartz (var.) Quartzite; R–Z. Realgar;
In 1986, California named benitoite as its state gemstone, a form of the mineral barium titanium silicate that is unique to the Golden State and only found in gem quality in San Benito County. [ 80 ] ^ Colorado is the only state whose geological symbols reflect the national flag's colors: red (rhodochrosite), white (yule marble), and blue ...
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Asterism is generated by reflections of light from twin-lamellae or from extremely fine needle-shaped acicular inclusions within the stone's crystal structure. [1] A common cause is oriented sub-microscopic crystals of rutile within the gem mineral. It occurs in rubies, sapphires, garnet, diopside, and spinel when a cabochon is cut from a ...