Emerald is the bluish green to green variety of beryl, a mineral species that includes aquamarine.

Emerald is the green to bluish-green variety of the beryl mineral family, which also includes aquamarine and other coloured beryl’s.

There is some debate among gem experts about what distinguishes an emerald from a less expensive green beryl. While some in the trade classify any green beryl with chromium as an emerald, most gemmologists, gemmological laboratories, and coloured stone dealers reserve the term "emerald" for stones with a sufficiently deep and saturated green colour. Stones with lighter hues are typically labelled as green beryl. However, there is still some disagreement about what constitutes the threshold between emerald and green beryl.

The Gemmological Institute of America (GIA) uses lab-graded comparison stones to assess whether a green beryl’s colour is rich and deep enough to qualify as an emerald.