Iron mineralogy and magnetic susceptibility of soils developed on various rocks in western Iran

The characterization of magnetic minerals and the relationship of these minerals to the magnetic susceptibility of soils that have developed on various parent materials can provide valuable information to various disciplines, such as soil evolution and environmental science. The aim of the study reported here was to investigate variations in the magnetic susceptibility (Chi ) of soils in western Iran due to differences in lithology and to examine the relationship of Chi to ferrimagnetic minerals. Eighty samples were collected from eight parent materials taken from both intact rocks and associated soils. The soil parent materials included a range of igneous and sedimentary rocks, such as ultrabasic rocks (Eocene), basalt (Eocene), andesite (Eocene), limestone (Permian), shale (Cretaceous), marl (Cretaceous), and the Qom formation (partially consolidated fine evaporative materials, early Miocene). The 80 samples were analyzed for Chi using a dual-frequency magnetic sensor and for mineralogy using X-ray diffraction (XRD). The highest Chi values were found in the ultrabasic rocks and associated soils, while the lowest Chi values were observed in the limestone rocks and associated soils. The pedogenic processes significantly enhanced the Chi values of soils developed on the sedimentary rocks due to the formation of ferrimagnetic minerals. In contrast, Chi values decreased as a result of pedogenic processes in soils developed on igneous rocks due to the dilution effects of diamagnetic materials, such as halite, calcite, phyllosilicates, and organic matter. The significant positive correlation between the XRD peak intensity of the maghemite/magnetite particles and Chi values confirmed that Chi values in soils are largely controlled by the distribution and content of ferrimagnetic minerals. These results show that Chi measurements can be used to quantify low concentrations of ferrimagnetic minerals in the soils of semiarid regions.