Resistivities have been measured on three pieces of dried boring rock cores at temperture ranges from 373K to 673K, in an air atmosphere. The resistivities and a dielectric constant that corrects the resistivities have been measured by putting a cylindrical rock piece between two electrodes. The results are as follows, 1) The resistivities of three pieces of rocks decrease as their temperatures rise. 2) The resistivity of each rock shows hysteresis. One of the reasons is that magnetite in the rock has changed into hematite. This change has been ascertained by observation of X-ray diffraction and magnetization. 3) Revised resistivity value by dielectric polarization is approximately half of the measured one. If resistivities of many kinds of minerals are measured, we can roughly estimate the dried rock resistivity by measuring the ratio of mineral components in the rock and the wet rock resistivity by measuring a resistivity of solution in the rock separately.
