Manganese oxide deposition in a hot spring microbial mat

The vertical distribution of manganese in a hot spring microbial mat has been analyzed chemically and structurally. Dissolved manganese concentrations were highest near the surface of the mat but decreased rapidly with depth. At the same time, an increase was observed in the amount of a solid manganese phase with an O/Mn ratio of 1.7 to 1.9. Electron microscopy and energy‐dispersive x‐ray spectroscopy of thin‐sectioned material revealed a variety of manganese oxide‐encrusted microbial forms. A 10‐Å tunnel structure prominent in the manganese precipitates and a 2.44‐Å d‐spacing in the corresponding electron diffraction patterns indicated that todorokite was the predominant manganese oxide polymorph formed within the microbial mat.