Abstract:
Geuda is a low-quality form of corundum and abundant in the most gem enriched regions
in Sri Lanka and can transfer into premium blue sapphires, similar to the natural in
appearance through heat treatments. The study intended to identify characteristic features
to distinguish heated geuda from natural sapphire using FTIR Spectroscopy. 53 geuda
samples were collected from five gem bearing localities Ratnapura, Ridiyagama,
Okkampitiya, Bakamuna, and Katharagama and heat treated up to 1800°C for the onehour soaking period under reducing environmental condition. Study samples were
subjected to FTIR analysis before and after the heat treatment and could identify the
development of a distinctive peak at 3310 cm-1
after treatment. This is due to the diffusion
of atmospheric Hydrogen back into the crystal and appears in the absorption spectrum as
an interstitial O-H bond in the corundum crystal structure. Further, two absorption bands
at 2342 or 2362 cm-1 which corresponds to atmospheric CO2 and CO2 gas in negative
crystals were observant in almost of the samples and as a direct response to CO2 gas in
negative crystals, the intensity of this particular peak is found to be significantly less for
Ridiyagama samples with respect to other localities. This reveals that the Ridiyagama
samples are with less CO2 trapped inclusions. Nevertheless, certain 2853 and 2924 cm-1
peaks were observed before and after heat treated stones due to the C-H bond resulted in
contamination. Furthermore, 3620 and 3697 cm-1
absorption bands related to Kaolinite
hydrous mineral inclusions have been disappeared with heat treatment. This concludes to
identify heat treated sapphires with 3310 cm-1 peaks and remaining of 3620 and 3697 cm-1
peaks verify it as a non-heat-treated sapphire. Hence, the FTIR technique could be
clarified as one of the best methods to identify heat treated blue sapphires.
Keywords: Heat treatment, FTIR analysis, Negative crystals, Absorption spectrum,
Inclusions
