Optical absorption, EPR, infrared and Raman spectral studies of clinochlore mineral

Abstract

Optical absorption, EPR, Infrared and Raman spectral studies have been carried out on natural clinochlore mineral. The optical absorption spectrum exhibits bands characteristic of Fe 2+ and Fe 3+ ions. A band observed in the NIR region is attributed to an intervalence charge transfer (Fe 2+–Fe 3+) band. The room temperature EPR spectrum of single crystal of clinochlore mineral reveals the dominance of Fe 3+ ion exhibiting resonance signals at g=2.66; 3.68 and 4.31 besides one isotropic resonance signal at g=2.0. The EPR studies have been carried out for a polycrystalline sample in the temperature range from 103 to 443 K and for a single crystal of clinochlore mineral in the temperature range 123–297 K. The number of spins ( N) participating in resonance at g=4.3 signal of the single crystal of clinochlore mineral has been calculated at different temperatures. The paramagnetic susceptibility ( χ) is calculated from the EPR data at different temperatures for single crystal of clinochlore mineral. The Curie constant and Curie temperature values are evaluated from 1/ χ versus T graph. The infrared spectral studies reveal the formation of Fe 3+–OH complexes due to the presence of higher amount of iron in this mineral. The Raman spectrum exhibits bands characteristic of Si–O–Si stretching and Si–O bending modes.