By using two-pulse excitation with phase-randomized pulses in an interferometer and analyzing the variance of the fluctuating fluorescence intensity, femtosecond beatings have been observed in the binary crystal pentacene/p-terphenyl, P/pTP at low phonon temperatures. The THz oscillations evolve from fluctuating quantum interferences prepared by the coherent superposition of different, electronic transition dipoles in spatially different constituents (O1-O4) of the pentacene impurity. The polarization beats can be explained by a model of uncoupled two-level systems including inhomogeneous dephasing as the predominant coherence relaxational pathway.