The color and identification of green tourmaline
Because the tourmaline homophonic "dispels evil spirits", it is very popular among people of all ethnic groups. Tourmaline is a colored mid-range gem next to diamonds, rubies, sapphires and emeralds. Green tourmaline is green due to its chrome and vanadium elements, and its pleochroism is light green and dark green. The birefringence is high, usually 0.018, and the highest is 0.039. Includes light green to dark green, yellow green or brownish green. Some colors may be dark or deep, and only visible through light. Dark green is almost opaque in the direction of the optical axis due to its strong dichroism, but can be improved by heat treatment. The best is emerald green, which was mistaken for emeralds in Europe and Brazil, showing its level of luxury. Currently only produced in Brazil and Madagascar. Gemstones similar to green tourmalines include diopside, emerald, and green beryl.
Green tourmaline ranges from strong green to green to yellow. Tourmaline is a birefringent gemstone with a refractive index difference from 0.018 to 0.040, typically 0.020; a refractive index of 1.62 to 1.64; and an optical characteristic of negative uniaxial.
The dichroic color of tourmaline is usually medium to strong color with the same color as its body color. Many gemstone crystals absorb more light in the lateral direction, and a gem crystal is light green from the side, but it may be observed from the long side. It is dark green and sometimes almost black. The clarity of many green tourmalines is clean and visible to the naked eye. Some of them exhibit cat's eye phenomenon. They often contain irregular, linear, liquid or gas inclusions that are present or staggered, and may have mirror-like gas-filled cracks. Growth tubes that are elongated or sometimes covered with tiny mineral crystals are also typical inclusions.
Some green tourmalines are distinguished by their bright colors and typical small size. They are produced by the province of ParaÃba, Brazil. The bright blue-green color produced by the copper elements is called the neon green dragonfly. Compared with the tourmaline, its color is saturated and the color tone is lighter. More than one carat of green and blue-green Paraiba tourmaline is rare and is the most valuable green tourmaline on the market. A similar blue-green tourmaline that is colored by copper impurities is also produced in Nigeria.
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