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[MGI31-P05] Analysis of major elements of magnetic minerals in sand fractions of soil for forensic examination: A preliminary study
Keywords:Forensic geology, Magnetic minerals, Analysis of major element
In the process of forensic examination of soil, particles are separated into several size fractions. Sand fractions are often divided into several subfractions of light minerals, heavy minerals and magnetic particles. The ratio of weight among these fractions is utilized as an index for discrimination. Light and heavy minerals are also observed by stereo and polarized microscopes for details. But magnetic particles are generally opaque, thus they can provide fewer information than others by microscopy.
Most of magnetic minerals in sand size are considered to be derived from primary minerals, and expected to be magnetite (Fe3O4) and ilmenite (FeTiO3). Iron of magnetite can be replaced by manganese, titanium and other elements. Chemical compositions of these minerals differ from place to place depending on the condition of crystallization.
Author analyzed these minerals in surface soil samples by electron dispersive X-ray analyzer (X-Max, Oxford Instruments) equipped on a scanning electron microscope (JSM-6610LV, JEOL, SEM-EDX). As a preliminary study, soil samples from different parent rocks, namely volcanic, granitic, and metamorphic rocks, were selected. Magnetic minerals were separated from sand fraction of soil using a magnet, and embedded in epoxy resin to be cut and polished. Then the polished samples were carbon coated and analyzed by SEM-EDX in a vacuum environment at 20 kV.
Iron, titanium and manganese were detected as major elements, and the ratio of these elements were plotted on triangle diagram. Magnetite was included in all samples, and content of titanium varied among samples. Manganese in ilmenites also showed variation. Comparison of distribution of plots between two samples is expected to be an index of discrimination of soil.
Most of magnetic minerals in sand size are considered to be derived from primary minerals, and expected to be magnetite (Fe3O4) and ilmenite (FeTiO3). Iron of magnetite can be replaced by manganese, titanium and other elements. Chemical compositions of these minerals differ from place to place depending on the condition of crystallization.
Author analyzed these minerals in surface soil samples by electron dispersive X-ray analyzer (X-Max, Oxford Instruments) equipped on a scanning electron microscope (JSM-6610LV, JEOL, SEM-EDX). As a preliminary study, soil samples from different parent rocks, namely volcanic, granitic, and metamorphic rocks, were selected. Magnetic minerals were separated from sand fraction of soil using a magnet, and embedded in epoxy resin to be cut and polished. Then the polished samples were carbon coated and analyzed by SEM-EDX in a vacuum environment at 20 kV.
Iron, titanium and manganese were detected as major elements, and the ratio of these elements were plotted on triangle diagram. Magnetite was included in all samples, and content of titanium varied among samples. Manganese in ilmenites also showed variation. Comparison of distribution of plots between two samples is expected to be an index of discrimination of soil.