Formation and decay of the center and its precursor in natural quartz: basics and applications

The center is a paramagnetic defect in quartz, where an unpaired electron is at an oxygen vacancy. The intensity of the center after heat treatment at 300 °C for 15 min (the heat treated center) indicates the amount of oxygen vacancies, which are precursors of the center. Using this technique, oxygen vacancies were found to be much more stable than other impurity centers, and to be useful for new applications, such as dating of granites, dating of uranium ores, estimating the temperature of heat treatment for stone implements, and provenance of eolian dust. The formation process of the oxygen vacancies in natural quartz has been in debate. Our recent pulsed ESR study indicates that they are probably created by natural beta and gamma rays.