Grunerite samples have been studied by Mössbauer and magnetic measurements to differentiate the hyperfine spectra of Fe2+ in the four non-equivalent sites. We can conclude: (i) TN = (46 ± 1) K; (ii) four different hyperfine fields are present at 4.2 K; (iii) between 8.2 K and 5 K, there is a sensitive change of the spectra; (iv) the grunerite magnetic structure consists of ferromagnetic chains coupled by weaker antiferromagnetic interactions. © 1983.