Dirac theory and the grand unified theories predicted the existence of magnetic monopoles in the universe. P. B. Price et al. pointed out the possibility to determine the flux of magnetic monopoles passing through the earth by counting the tracks created by monopole-nucleus bound state in mica. Natural muscovite mica exploited from Xinjiang First Mica Mine in China was selected as detectors and dated by the fission track method. The fission track age of 129±8 Ma was obtained

which was considered to be the approximate age for the mica to record tracks of monopole-nucleus bound state.