Development of magnetic soil from ferroan dolomite

Abstract

An occurrence of maghemitic soil in association with ferroan dolomite in Minas Gerais is characterized by X‐ray diffraction, magnetization measurements and Mössbauer spectroscopy. Altered layers on outliers of dolomite, which has composition (Ca 1.04 Mg 0.83 Fe 0.11 Mn 0.02 )(CO 3 ) 2 indicate the weathering sequence: ferroan dolomite → calcite + poorly‐crystallized ferric hydroxide → maghemite + hematite + goethite. The spontaneous magnetization of the maghemitic soil (65 wt% Fe 2 O 3 ) is 8.8 JT −1 kg −1 ; the magnetization of the soil maghemite itself is estimated to be 25±5 JT −1 kg −1 , which is greatly reduced from the value for pure maghemite because of isomorphous substitution.