EPR, optical, infrared and Raman spectral studies of Actinolite mineral

Electron paramagnetic resonance (EPR), optical, infrared and Raman spectral studies have been performed on a natural Actinolite mineral. The room temperature EPR spectrum reveals the presence of Mn²⁺ and Fe³⁺ ions giving rise to two resonance signals at g=2.0 and 4.3, respectively. The resonance signal at g=2.0 exhibits a six line hyperfine structure characteristic of Mn²⁺ ions. EPR spectra have been studied at different temperatures from 123 to 433 K. The number of spins (N) participating in the resonance at g=2.0 has been calculated at different temperatures. A linear relationship is observed between log N and 1/T in accordance with Boltzmann law and the activation energy was calculated. The paramagnetic susceptibility (χ) has been calculated at different temperatures and is found to be increasing with decreasing temperature as expected from Curie’s law. From the graph of 1/χ versus T, the Curie constant and Curie temperature have been evaluated. The optical absorption spectrum exhibits bands characteristic of Fe²⁺ and Fe³⁺ ions. The crystal field parameter Dq and the Racah parameters B and C have been evaluated from the optical absorption spectrum. The infrared spectral studies reveal the formation of Fe³⁺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 MgOH translation modes.