Mineralogical and Gemmological Profiling of Corundum: Distinguishing Karur Natural Rubies from Synthetic Counterparts

We present a comparative study of natural gem-quality ruby from the Karur region, Tamil Nadu, and synthetic ruby powders prepared via sol-gel thermolysis. Using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and gemmological analysis, we characterized the structural, chemical, and physical properties of these materials. XRD analysis confirmed orthorhombic crystal structure in all samples, with natural ruby showing significantly larger crystallite sizes (372.5-425.2 nm) compared to synthetic samples (29.9-47.2 nm). FTIR spectroscopy revealed characteristic absorption bands at 3600-3400 cm⁻¹ (OH stretching), 1650 cm⁻¹ (OH bending), and 430- 635 cm⁻¹ (metal-oxygen bonds), confirming the corundum framework with chromium incorporation. SEM imaging showed dense microstructures with distinct grain morphologies between natural and synthetic samples. Gemmological properties of natural ruby included Mohs hardness of 9, refractive index of 1.762-1.778, density of 3.97-4.05 g/cm³, and strong carmine red fluorescence. Our findings demonstrate that high-purity synthetic ruby can be produced cost-effectively at relatively low temperatures, offering insights for both gemstone authentication and industrial applications.