Experimental Study of the Electrical Properties of A Ghanaian Metamorphic Rock Using Resistivity Variation with Temperature

Measurement of resistivity of typical Ghanaian rocks like hornblende garnet gneiss with temperature variations usually reveal that from 300 K to around 430 K, resistivity increases linearly with temperature to a peak of a few MΩm, after which it drops exponentially with temperature. The temperature dependence of resistivity for four samples of hornblende garnet gneiss has been measured, in the temperature range from 300 K to about 500 K for both increasing and decreasing temperatures, to elucidate the nature of electric current been carried in the rocks. The first sample was not given any treatment. The second sample was baked to 1000 K for 30 minutes to drive out all pore fluids and allowed to cool to 300 K in a dry environment. The third sample was dried for 14 days with silica gel. Lastly, the fourth sample was soaked in CaSO₄(Calcium Sulphate) solution for 21 days. Temperature hysteresis in each case was observed in the resistivity measurements. Except the sample, which showed semiconductor - semi-metallic transition in resistivity at certain temperatures. All the samples showed increasing resistivity with increasing temperature to certain peaks, beyond which the resistivity decreased exponentially with temperature. The energy gaps for all samples ranged between 1.20 eV and 1.1eV. The accuracy of the resistance measurements was + 0. 1%. The semiconductor - semi-metallic transition in the baked sample vanished when left in the air to absorb moisture. The results obtained fully satisfies the aim of the experiment. The semiconductor-semi-metallic transition observed can be investigated for application in other areas of study.