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Impurity paramagnetic ions Mn2+ and high spin Fe3+ (S = 5/2) are shown to be very informative paired spin labels to investigate structural transformations in natural aluminosilicate clay minerals by ESR spectroscopy. Second derivative ESR (SD ESR) enables to detect minor narrow lines of the ions against the background of intense broad lines of other paramagnetic impurities. Complex SD ESR spectra of the ions are explained by the Jahn-Teller effect and hyperfine interactions with OH-groups. SD ESR spectra before and after heating (620 and 900°C) proved transformations of octahedral crystal cells accompanied by the loss of the OH-groups, displacement of the ions to equivalent positions. [ABSTRACT FROM AUTHOR]