Static and resonant magnetic properties of halotrichite

Halotrichite has been investigated with the help of scanning electron microscopy, X-ray spectral microanalysis, vibrating sample magnetometry and electron paramagnetic resonance methods. In the crystal structure of the studied sample (Fe$_{0.75}$Mg$_{0.25}$)Al$_2$(SO$_4$)$_4\times22$H$_2$O, a quarter of the position of the divalent ion is occupied by Mg$^{2+}$. The static magnetic properties of this mineral are completely determined by ferrous ions. At the same time, the electron paramagnetic resonance spectrum indicates the presence of divalent manganese ions in the sample in quantities that cannot be determined by X-ray spectral microanalysis.