ウェブBeryl (/ ˈ b ɛr əl / BERR-əl) is a mineral composed of beryllium aluminium silicate with the chemical formula Be 3 Al 2 Si 6 O 18. Well-known varieties of beryl include emerald and aquamarine . Naturally occurring hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare.