A combined Raman and IR spectroscopic study has been carried out on natural cordierite samples from Kalahandi district, Odisha to understand the effect of Mg-Fe2+ exchange on Raman peak shift and to identify the volatile species within these cordierite crystals. In the field, the cordierites are hosted by silica-saturated quartz-feldspathic rocks, mafic granulites and also by the silica-undersaturated Mg-Al granulites. X-ray Diffraction (XRD), Raman spectroscopy and microprobe analyses were initially used to characterize the samples and to obtain chemical composition respectively. XRD of the gem quality cordierite reveals perfect orthorhombic symmetry, supported by Raman analyses that deduce the extent of Al-Si ordering in this mineral. Microprobe data indicate that most cordierites are Mg-rich (XMg = 0.93-0.94), however, a variation in Mg/Fe concentration of cordierite from different locations is observed. The samples also show high Na content that are associated with quartzo-feldspathic rocks intruded by pegmatites, than that of the Mg-Al granulites. This result suggests temperature variance in cordierite crystallization among different host rocks. Raman spectra of these cordierites define structurally resolved Raman vibrational modes where the magnitude of peak shift of most bands towards lower wavenumber than pure Mg-cordierite is proportional with Fe concentration, and are linked with the extent of Mg-Fe exchange within cordierite structure. FTIR study confirms the presence of both type-I and type-II waters along with significant amount CO2 as channel constituents, however, type-I H2O and CO2 concentrations vary within a single crystal. The FTIR spectroscopic evidence strongly supports a H2O and CO2 bearing fluid composition during crystallization of cordierite from these localities.

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Orissa is an important area for gem variety of corundum deposits in India. Spectroscopic studies, such as ESR, OAS on samples from Sardapur, Orissa, were carried out to ascertain the colour cause of corundum. Electron spin resonance (ESR) spectroscopic study was carried out on the samples to detect the presence of paramagnetic ions i.e. Fe2+, Fe3+, Ti4+, Cr3+ and V3+ etc. The variable temperature experiment carried out to observe the effect of heating on peak valence state change in paramagnetic ions. Samples were cut and polished to obtain the optical absorption spectrum (OAS) to detect the colour causing transition ions/defect centres. The samples of gem variety were step heated up to 300°C for colour enhancement studies. EPMA analysis has revealed the low chromium concentration in the rubies. The varying hues of red in the corundum are due to the presence of bivalent and trivalent iron and charge transfer process along with Cr3+ absorption in the 550 nm region.