Based on the observations in rhodonite (Mn,Ca)s- [Si5015], errors in the periodicity of the tetrahedral chains in babingtonite were expected; they are confirmed by high-resolution electron microscopy. These errors are arranged mainly into planar chain periodicity faults (CPF). Deviations of the faults from planarity, such as terminations and alterations of the fault units, have been found. 57Fe M6ssbauer studies show that the frequency of CPF's is not controlled by positional disorder of the cations.