Emeralds, the birthstone of May, are a distinctly green specimen of the beryl family. Add too much blue, and they become aquamarine. Add too much yellow, and they become heliodor. But the rich, deep green of an emerald is unmistakable, and emeralds have long been collected for their value and their rarity. Your jewelry wardrobe isn't complete without at least one representative of this beautiful gemstone.