The refractive indices of the synthetic overgrowth on the beryl seeds of Lechleitner synthetic emeralds show a linear correlation with the chromium content of the coating. In a sample with refractive indices of no=1.580, ne=1.572a, Cr203, content of 3.99% was found; a stone with no=1.610, ne=1.601 contained 10.01 % Cr2O3. Very broad, faint shadow edges on the refractometer in one sample were caused by an inhomogeneous distribution of Cr2O3,--between 7.64% and 13.20%--in the synthetic emerald overgrowth. From these experiments, it is evident that the higher the chromium content in the overgrowth, the darker the coating (and, therefore, the overall appearance of the stone) will be.
