According to Munsell's color system theory, the color grades of emeralds are divided into light (light green), medium (medium green), thick (dark green), fresh (bright green) and dark (dark green).

The main chromogenic elements of emeralds are Cr and V. When electrons around chromogenic ions absorb some visible light, the gem will appear green. Different contents and types of chromogenic elements lead to slightly different colors of emeralds. For example, the emerald in Colombia has a low Fe content, so the green color will appear bright, while the emerald in Zambia has a high Fe content and a low V content, so the green color tone is darker.

Extended data:

1. Emerald is a beryllium aluminum silicate mineral. Several varieties of it have different colors, such as light blue (called aquamarine), dark green (called emerald), golden yellow (called beryl) and pink (called cesium beryl). Honey yellow is more common. Emerald is generally hexagonal columnar crystal, and its color is mostly green.

2. Emeralds are mostly light green and pink when rich in cesium, which is called rose emeralds. When containing chromium, it is bright emerald, which is called emerald. When it contains ferrous iron, it is light blue and is called aquamarine. When it contains trivalent iron, it is yellow and is called yellow emerald.

Emerald is the birthstone of May, symbolizing luck and happiness. Wearing it will bring people a lifetime of peace. This is also the 55th wedding anniversary stone. Emerald is a very old gem, which was used as jewelry in ancient Egypt.

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