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Emerald is defined by its green color. To be an emerald, a specimen must have a green color that falls in the range from bluish green to green to slightly yellowish green. To be an emerald, the specimen must also have a rich color. Stones with weak saturation or light tone should be called "green beryl." If the beryl's color is greenish blue then it is an "aquamarine." it is greenish yellow it is "heliodor."
This color is a source of confusion. Which hue, tone, and saturation combinations are the dividing lines between "green beryl" and "emerald"? Professionals in the gem and jewelry trade can disagree on where the lines should be . Some believe that the name "emerald" should be used when chromium is the cause of the green color, and that stones colored by vanadium should be called "green beryl."
Calling a gem an "emerald" instead of a "green beryl" can have a significant upon its price and marketability. This "color " exists within the United States. In some other countries, any beryl with a green color - no matter how faint - is called an "emerald."