Extended Abstract: Three useful parameters are readily determined from the Mössbauer interaction; the isomer shift, the nuclear electric quadrupole splitting, and the nuclear magnetic dipole splitting. The isomer shift, which is related to chemical bonding and changes in valence, and the quadrupole splitting, which is sensitive to structural environment, are the prime consideration in this work. The isomer shift is a function of the charge density of electrons at the nucleus. The quadrupole splitting depends on the asymmetry of the electric field at the nuclear site. The splitting for Fe3+ is caused by the neighboring ions, but for Fe2+ the relevant field gradient is related primarily to the electron distribution in the iron ion. Previous studies have established the following ranges for the values of these parameters: the isomer shift (measured from the center of the iron metal pattern, −0.25 mm/sec in our work) for Fe3+ from 0 through +0.5 mm/sec and for Fe2+ from 0.40 through 1.7 mm/sec. Table 1* summarizes the data obtained in the present study.
Mössbauer absorption spectrography can be used to establish the presence of Fe2+ and Fe3+ in clay minerals. In the sheet structure silicates, octahedrally coordinated iron can be distinguished from tetrahedrally coordinated iron. Siderite and goethite, common contaminants of the clay minerals, can usually be detected. Goethite has a well-organized structure, though, due to its fine grain size, may appear to be amorphous to X-rays. The various families of clay minerals show minor differences in isomer shift and quadrupole splitting values.