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EMERALD:PHYSICAL CHARACTERISTICS:VARIETY OF: Beryl , Be3 Al2 Si6 O18 . USES: Gemstone. BIRTHSTONE FOR: May COLOR: various shades of green. INDEX OF REFRACTION: 1.57 - 1.60 BIREFRINGENCE: 0.004 - 0.008 HARDNESS: 7.5 - 8 CLEAVAGE: one direction, poor. CRYSTAL SYSTEM: hexagonal Pleochroic: weak Emerald is the green variety of the mineral beryl. Other gemstone color varieties that belong to beryl include aquamarine, morganite, heliodor, and goshenite. Other colors of beryl are simply referred to by their color, such as red beryl. The wonderful green color of emerald is unparalleled in the gem kingdom. Emerald's precious green color is caused by small amounts of chromium and enhanced by traces of iron. Unlike other beryls, emeralds often contain inclusions and other flaws. These flaws are not looked on as negative aspects for emerald like they would be for other gemstones. Indeed, these flaws are considered part of the character of the stone and are used to assure the purchaser of a natural stone. However, fractures and inclusions are so common in emeralds that their toughness is affected - emeralds tend to break more easily than other beryls. Emerald is mined around the world, although certain localities provide the best gemstones. Columbia is especially notable, producing fine deep-green emeralds of excellent transparency. Brazil and Pakistan are other notable sources of fine emeralds.
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