The name is diverted from the chemical element beryllium, the original expression came from india but had a different meaning. That appears strange but its similar to the german word "brille" which comes from the word beryllium and is now made of glass or plastic.
The hardness is 7,5-8 and the chemical structure is: Al2Be3(Si6O18).
The colorgiving elements are various and not only metals or metal oxides. for example the davidsonite is light yellow to greenish yellow by nitrogenium.
Optical effects are asterism and chatoyance (stars and catīs eyes).
Several gemstones belong to the beryl-group:
Heliodor (yellowish to blueish green)
Morganite (light pink to apricot)
There is also a green variety which is colored by chrome and not that suitable for gemstones because itīs fragile and interfered with inclusions and cracks, itīs called "emerald" and you should only buy it if you need some oil.