The chemical composition of emerald is Be3Al2Si6O 18, and its crystal belongs to hexagonal silicate mineral with ring structure. Crystals are usually hexagonal cylinders with longitudinal stripes on the surface. Aggregates are sometimes clustered or needle-shaped, and sometimes they can form giant crystals, which can be up to 5 meters long and weigh 18 tons. Mostly light green, pink when rich in cesium, called rose emerald; When containing chromium, it is bright emerald green, called grandmother; When it contains ferrous ions, it is light blue and is called aquamarine; When it contains trivalent iron, it is yellow and is called yellow emerald. Glass luster, not perfect cleavage. Mohs hardness is 7.5-8, and specific gravity is 2.6-2.9.

Emerald is the representative of green transparent stone. When people talk about bright colors, they will use the expression "emerald green". Emerald has a low specific gravity, so even if the particles are small, they still look larger than diamonds or rubies with the same number of carats, which is its characteristic. In emeralds, there are often many inclusions such as "Moxi" visible to the naked eye, so they are often mistaken for defects. In fact, this kind of substance is completely different from the defects that will damage the value of gems. It is an inevitable inclusion in the process of crystal formation, and it can also be regarded as evidence of natural gemstones, and it is also an element that casts a mysterious veil on emeralds. But this is also related to the degree, too much damage to the beauty of the gem is not good. Emerald cuts are usually rectangular and occasionally square. This is because emeralds and sapphires are hexagonal columnar crystals, and cutting in this way can exert the greatest benefit and show the most beautiful side.