Medium to dark green beryl which derives its color from chromium (some gemologists argue that dark green beryl colored by vanadium should be called emerald, and others insist that chromium must be present).

The best known sources include Colombia, Zambia. Almost all emeralds contain numerous small inclusions and fractures that promote fragility. Most stones on the market are impregnated with oils, waxes, or other substances to mask the fractures and sometimes enhance color.

Such stones should never be cleaned with ultrasound, as it may remove or damage the impregnating substance. Emeralds of fine color and clarity can be quite expensive.