Characterization of pebble surfaces coated with biogenic manganese oxides by SIMS, XPS and SEM

The biogenic manganese oxide coating on the surface of a riverbed pebble was analyzed by means of secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). SEM observation combined with energy-dispersive X-ray spectroscopy (EDXS) confirmed that the coating consisted mainly of manganese oxide (thickness, 5 μm to a few tens of micrometers). SIMS and XPS analyses of the pebble surface suggested that the coating also contains iron oxides, silicate minerals and carbonaceous materials. The Mn 2p photoelectron spectrum indicated that the manganese oxide consists mainly of Mn(IV). Depth profiling by SIMS showed that the secondary ion intensities of Mn and Si increased and decreased, respectively, with sputtering time, which confirmed that the surface of the coating contains silicate mineral particles. In addition, the depth profile of Mn showed an oscillating pattern, suggesting a fine structure of the biogenic manganese oxide coating.