• journal_title：American Mineralogist
• Contributor：Sylvain Grangeon ; Bruno Lanson ; Naoyuki Miyata ; Yukinori Tani ; Alain Manceau
• Publisher：Mineralogical Society of America
• Date：2010-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2010.3516
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：95
• issue：11-12
• firstpage：1608
• section：Articles

The crystal structures of biogenic Mn oxides produced by three fungal strains isolated from stream pebbles were determined using chemical analyses, XANES and EXAFS spectroscopy, and powder X-ray diffraction. The fungi-mediated oxidation of aqueous Mn²⁺ produces layered Mn oxides analogous to vernadite, a natural nanostructured and turbostratic variety of birnessite. The crystallites have domain dimensions of ~10 nm in the layer plane (equivalent to ~35 MnO₆ octahedra), and ~1.5–2.2 nm perpendicularly (equivalent to ~2–3 layers), on average. The layers have hexagonal symmetry and from 22 to 30% vacant octahedral sites. This proportion likely includes edge sites, given the extremely small lateral size of the layers. The layer charge deficit, resulting from the missing layer Mn⁴⁺ cations, is balanced mainly by interlayer Mn³⁺ cations in triple-corner sharing position above and/or below vacant layer octahedra. The high surface area, defective crystal structure, and mixed Mn valence confer to these bio-minerals an extremely high chemical reactivity. They serve in the environment as sorption substrate for trace elements and possess catalytic redox properties.