gems, beryl, aquamarine, emerald, morganite, heliodore, goshenite

The colours of the beryl varieties aquamarine, heliodor, golden beryl, goshenite and morganite are caused by the interaction of different absorption processes, which in turn are caused by traces of iron and manganese on different positions in the crystal lattice. The exact region of transmission between the absorption bands is formed by the overlapping of spin-allowed crystal field bands of Fe²⁺, the Fe²⁺/Fe³⁺-IVCT, as well as the absorption in the blue-violet spectral region. The exact shape of this OMCT-band system depends on the contents of Fe²⁺ and Fe³⁺. Spin-allowed absorption bands of Mn³⁺ produce an absorption of the blue and green and a transmission window in the red spectral region. Additional traces of chromium and vanadium can influence the colour as well.