Why are the gems of the same substance different in color?

From the perspective of crystal field theory. Under the influence of the surrounding crystal field, the energy levels of the five degenerate D orbitals are split by doped metal ions. At this time, the split D orbit can allow d-d transition, and can absorb visible light when illuminated, showing complementary colors. Color mainly depends on the splitting energy of d orbit. One of the reasons is that the symmetry of doping sites may be different, and the splitting mode and energy of crystal field are also different due to the different formation methods of gems. In most cases, the metal ions are different, which have great influence on the splitting energy for two reasons. In addition, as well as the contribution of surrounding ligands (ions), the splitting energy of different ligands of the same metal in the same symmetric environment is also different. Reason 3: The above three reasons lead to color difference.