Room-temperature optical absorption spectra, microprobe analyses and X-ray cell parameters of a manganese-bearing chlorite from Långban, Sweden are presented. The optical absorption spectra are characterized by four broad and intense absorption bands at 23300, 21900, 19700 and 11300 cm−1, which are assigned to Mn3+spin-allowed d-d transitions. The structure of the crystal field spectra of Mn3+in chlorite and the obtained crystal field splitting parameter, 10Dq = 16000 cm−1, indicate that Mn3+is located at a six-coordinated site, where the mean Mn3+-ligand bond distance is ∼ 0.200 nm and the site symmetry is lower than C2v. The most likely location of Mn3+in the chlorite structure is the small M(4)-site of the brucite-type layer.