The crystal structure of cummingtonite-(P21/m) was characterised by single-crystal structure-refinement, infrared spectroscopy and 57Fe Mössbauer spectroscopy. Previous cummingtonite-(P21/m) specimens characterised have Mn2+ as the dominant constituent at M(4) but this amphibole has Fe2+ dominant at M(4). The formula of the amphibole was corrected for minor exsolved calcium-amphibole and is (Mg5.66Fe2+1.28Mn0.06)Σ7.00Si8.00O22(OH)2. The crystal structure (a = 9.4885(19), b = 18.040(4), c = 5.2891(11) Å, β = 102.06(3)°, V = 885.4(3) Å3, space group P21/m and Z = 2), was refined to an R1-index of 3.34% for 2338 observed reflections. Site-occupancy refinement gave the following site-populations: M(1) = 1.972(8) Mg + 0.028 Fe2+, M(2) = 2.000 Mg, M(3) = 0.989(6) Mg + 0.011 Fe2+, M(4) = 0.815(8) Mg + 1.125 Fe2+ + 0.060 Mn2+ apfu. Infrared spectroscopy in the principal (OH)-stretching region shows two peaks, at 3367 and 3652 cm–1, that were assigned to the local arrangements M(1)MgM(1)MgM(3)Mg–OH and M(1)MgM(1)Fe2+ M(3)Mg–OH (≈ M(1)MgM(1)MgM(3)Fe2+–OH) with relative intensities in accord with the refined site-populations. 57Fe Mössbauer spectrum shows three quadrupole-split doublets with parameters indicative of octahedrally coordinated Fe2+ at M(4) and M(1,2,3), and octahedrally coordinated Fe3+ that occurs in exsolved calcium amphibole. All three techniques indicate a small amount of Fe2+ at M(1,2,3) despite the fact that there is more than sufficient CMg to completely fill the M(1,2,3) sites: 5.66 Mg pfu. Issues involving the current and possible future nomenclature and classification of the magnesium-iron-manganese amphiboles are discussed in detail.