Characterization of iron accumulated in the teeth of chiton by X-ray absorption fine structure technique

Abstract

The chemical form of iron accumulated in the teeth of chitons was investigated by electron microprobe analysis (EPMA), X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) techniques. Two-dimensional elemental mapping by EPMA showed two distinct parts in a tooth of chiton : an Fe-rich part and a Ca-rich part. The Fe-rich part occupied the sharp edge of the tooth, which is actively used in scratching food, whereas the Ca-rich part was located at the opposite side of the tooth, and contained Ca, P and Mg as major elements. The inner immatured teeth on a radula gradually became matured toward the chiton's mouth, and their color changed in the following order: brown, gray, red and finally black. The results of XRD indicated that a crystalline material in the gray, red and black teeth was magnetite (Fe3O4). On the other hand, the Fe KXANES spectra of each group of teeth showed that FeOOH was another component of the Fe-rich part of the teeth. The spectra suggested that the valency of iron partially changed from Fe(III) to Fe(II) along with the maturation of the teeth. The FeOOH was amorphous to X-rays, and was most likely to be a precursor of crystalline magnetite in the teeth. © 1995, The Japan Society for Analytical Chemistry. All rights reserved.