Minerals and Metals in Ancient India v2.c43.s3.t11.9

v2.c43.s3.t11.9

It has been conclusively proven that the deep blue colour of lazurite is due to the transition among the orbitals of the 19 outer electrons of the S₃⁻ polysulphide units in the mineral. (Nassau, 1983: 149) Pale blue samples when raised to a dull red-heat, assume fine dark blue colour possibly because a larger proportion of sulphur atoms re-align themselves to form S₃⁻ ions as in artificial ultramarine.