Thermal Decomposition of Natural Actinolite: A High Temperature Electrical Resistivity Study

We report here the first observation of a thermally induced irreversible decomposition in natural actinolite, collected from Santaveri, Karnataka, by using DC electrical resistivily measurements upto 1100K. The electrical resistivity of the actinolite sample is found to be 4 X 10¹¹ Ohm-cm at room temperature and pressure. The temperature dependence of the electrical resistivity of the samples exhibits an Arrhenius behaviour ρ = ρ_n exp(ΔE/kT) in the region 300-700 K with an activation energy of 0.76 eV. At 770 ± 5 K a first-order increase in resistivity from 7.93 X 10³ to 3.55 X 10¹⁴ ohm-cm has been observed, which is due to decomposition of the sample. In the temeprature region 775-1100 K, the value of the activation energy is found to be 0.20 eV. X-ray diffraction studies on the thermally quenched samples indicate that the decomposed phase is a mixuture of cummingtonite, clinopyroxene, plus quartz and water vapour as associated products. These breakdown products are found to be identical to those proposed by Cameron (1975), and contrary to the mineral assemblage of fayalite-hedenbergite-pyroxene-quartz-vapour as proposed by Ernst (1966).