Emerald is defined by its green color. To be an emerald, a specimen must have a distinctly 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 it is greenish yellow it is " heliodor ." This color definition is a source of confusion.
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