The infrared absorption of the rubies from Mong Hsu was analyzed in order to classify the absorption features recorded. In the mid-infrared region, it was possible to distinguish two seperate types of spectra. The first type was recorded in non-heat-treated ruby samples in the region from 1990 to 3400 cm, identifying inclusions of diaspore. The second type was recorded in heat-treated ruby samples in the region from 3100 to 3600 cm-1, indicating structurally bonded OH groups. Detailed for the first time in corundum, the building of OH groups i s accomplished as a direct result of the dehydration of diaspore inclusions, demonstrated through heat treatment experiments.
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