Effects of Cr3+ impurity concentration on the crystallography of synthetic emerald crystals

Flux method has been adopted for the synthesis of emerald crystals using PbO–V2O5 as a flux in order to study the crystallography of the synthetic crystals. In general, the hue of green color of emerald deepens with the addition of Cr3+. The molar volume of the synthesized crystals was found to increase with the incorporation of Cr2O3 dopant. The substitution of Cr3+ for Al3+ in the octahedral sites of beryl results in the expansion of a-axis, while c-axis remains nearly unchanged. The maximum Cr2O3-content allowed in the crystal lattice of emerald has been found to be about 3.5 wt%. When the doping Cr2O3-content exceeds 3.5 wt%, a significant anomaly in lattice parameters starts to take place, accompanying the precipitation of an unknown phase in the emerald matrix.