Thermal decomposition of natural actinolite: A high temperature electricalresistivity study

We report here the first observation of a thermally induced irreversible de composition in natural actinolite, collected from Santaveri, Karnataka, by using DC electrical resistivity measurements upto 1100K. The electrical res istivity of the actinolite sample is found to be: 4 X 10(11) Ohm-cm at room temperature and pressure. The temperature dependence of the electrical res istivity of the samples exhibits an Arrhenius behaviour rho = rho(o) exp(De lta E/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 7.93x10(3) to 3.55x10( 4) ohm-cm has been observed, which is due to decomposition of the sample. I n 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 sa mples indicate that the decomposed phase is a mixuture of cummingtonite, cl inopyroxene, plus quartz and water vapour as associated products. These bre akdown products are found to be identical to those proposed by Cameron (197 5), and contrary to the mineral assemblage of fayalite-hedenbergite-pyroxen e-quartz-vapour as proposed by Ernst (1966).