VACANCY-ASSOCIATED TYPE ESR CENTERS OBSERVED IN NATURAL SILICA AND THEIR APPLICATION TO GEOLOGY

Vacancy-type ESR centers (E', peroxy centers, etc.) in silica often increase by thermal annealing due to the diffusion of electrons or holes. Furthermore, the E' center increases also by grinding or crushing because the bonds between oxygen and silicon ions are cut and electrons are trapped at the oxygen vacancy sites on the surfaces of cracks. The E' center formed on the surface of crystal always decreases by heating above about 150-degrees-C. The relationship between the intensity and microwave power shows that the E' center on the surface of crystal exists in an inhomogeneous system implying local magnetic fields, and that it has lower absorptivity of microwaves than the E' center as a point defect in crystal. The E' center on the surface of crystal could be used for the dating of fault movements near the surface of the earth, while the peroxy center is possibly a strain gauge.