Emeralds are a variety of the mineral beryl, which is a beryllium aluminum cyclosilicate. The green color of emeralds comes from trace amounts of chromium and/or vanadium present in the crystal structure of the beryl.
The presence of these elements is responsible for the characteristic vivid green hue that distinguishes emeralds from other varieties of beryl. The presence of other impurities and inclusions, such as fractures or growth patterns, can also affect the appearance and value of emeralds.