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The value of any gemstone depends on one or more of four attributes: cut, color, clarity and size. Since large stones are rarer than small ones, the value of a gemstone rises exponentially with its carat weight.


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Rubies are a relatively rare gemstone. Burmese rubies command the highest price. Stones that are recut or even exported before cutting are worth more per carat than native-cut rubies. According to the International Gem Society, clean, top-color gems command a retail price of $1,000 to $3,000 per carat.


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In general, the deeper and more vivid an emerald's color, the higher its value per carat. Most emeralds have small fissures called inclusions; the fewer the inclusions, the more expensive the emerald. A large, deep-green emerald with relatively few inclusions and little secondary coloration may fetch tens of thousands of dollars per carat.


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Diamonds have steadily increased in value and show no signs of slowing. The pricing of diamonds can range anywhere from $1,000 to $40,000 per carat, depending on clarity, cut and color.