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Feitknechtite mineral

Feitknechtite is the manganese(III) oxide hydroxide mineral beta-MnOOH, listed as approved with the notation 1968 s.p. in the September 2026 IMA-CNMNC list. That notation is retained as authority metadata, not converted into an invented accession. Post et al. (2023) resolve a monoclinic C2/m structure, superseding older trigonal descriptions; the species is distinct from manganite and groutite and from Mn(II) pyrochroite. The mechanism below concerns a source-assigned transient mixed-phase product. No criticality is inherited from manganese.

Microbial & Biochemical Mechanisms (1)

Transient feitknechtite-assigned phase during Geobacter-associated manganese oxide reduction

biomineralization Microbial

Associated Organisms: Geobacter sulfurreducens (NCBITaxon:35554)

During anaerobic incubation of synthetic cobalt/nickel-bearing manganese oxide with a Manchester Geobacter sulfurreducens culture, the source assigns feitknechtite reflections to solids sampled after 1 and 17 hours, alongside pyrochroite and rhodochrosite. Feitknechtite is not labelled in the 72-hour pattern. The phase assignment and valence changes support a culture-associated Mn(III)-bearing intermediate, but do not prove that every electron passes through crystalline feitknechtite, that its absence means complete conversion, or that a particular cytochrome is causal. No purified product yield or industrial recovery is demonstrated.

Experimental Context & Analytical Limits:
Buchanan's laboratory culture collection supplied Geobacter sulfurreducens without a strain accession. Living cells were grown anaerobically at 30 degrees C with acetate/fumarate, harvested in late logarithmic phase and washed three times in 30 mM bicarbonate buffer at pH 7.1 under N2:CO2 80:20. The experiment used a 5 mL aliquot of synthetic Co/Ni-asbolane suspension (stock nominally 2 mmol/L Mn in 10 mM bicarbonate at circumneutral pH), added sodium acetate at reported 10 mM and cells to final OD600 0.6, incubated anaerobically in the dark at 30 degrees C. The added cell volume and precise final mineral concentration are not reported. The synthetic feed was precipitated from Co/Ni/Mn chlorides with KMnO4/KOH, washed in alkaline NaCl and stored at 4 degrees C. Its asbolane designation is source-assigned; the thesis acknowledges structural uncertainty and mixed Mn oxidation states. No-cell controls contained the same mineral suspension and acetate. Sampling used aseptic anaerobic handling; residual slurry was dried anaerobically before powder XRD. No-cell diffraction patterns, killed-cell mineral controls or a demonstrated drying-independent phase assignment are supplied.
Curated Evidence Points:
Chapter 4 Figure 4.2b-c and Results on printed pages 127-128 assign feitknechtite at 1 and 17 hours. Its reflections are not labelled in Figure 4.2d at 72 hours, while pyrochroite/rhodochrosite remain. Mn(III) persists in the bulk spectral fit at 72 hours, so loss of a labelled diffraction peak must not become complete Mn(III) reduction or quantitative disappearance. The proposed two-step pathway is narrower evidence than a demonstrated compulsory enzymatic sequence.
Chapter 4 methods and Figure 4.1 (printed pages 123-128) show cell-associated dissolved-metal release above no-cell controls, followed by declining aqueous Mn between 17 and 72 hours. These are centrifuged-supernatant ICP-MS measurements, not direct aqueous valence measurements or isolated product recovery. Biological ICP-MS samples at 1 and 17 hours are described as triplicate, 72 hours as one sacrificial bottle, and controls as duplicate; Figure 4.1 includes 24 hours but its replication is unspecified. Neither aqueous loss nor retained metal establishes allocation to this particular mineral.
Figure 4.2 (printed page 131) presents labelled mixed-phase patterns without quantitative phase refinement, phase-specific mass balance or a matched no-cell mineral time series. Pyrochroite and feitknechtite have overlapping low-angle peaks, so the accepted claim is the author's assignment, not independently re-refined purity. Figure 4.3 and pages 129-130 show cell-associated particles and heterogeneous elemental spectra; the 17-hour laths are only tentatively linked to the two phases. Elemental co-occurrence does not identify a unique cobalt/nickel host or prove lattice incorporation.
Figures 4.4-4.8, the tables on printed pages 146-147 and Appendix 4.1-4.2 support a heterogeneous shift toward lower manganese valence. Fitted oxidation-state fractions carry the author's stated 10% error and differ substantially between surface-sensitive bulk measurements and spatially restricted transmission SXM. Only one imaged region per time point was possible, and coherent SXM data are absent at 72 hours. These are spectral fractions, not mineral abundances or conversion yields. A sequential one-electron pathway and direct cell-surface cytochrome participation remain interpretations; no enzyme perturbation or phase-specific electron-transfer test was performed.
Source inconsistencies remain unresolved: the tables discussed as 4.1/4.2 are printed as 6.1/6.2; the 17-hour co-located Mn average differs between the main table and appendix/text; regional counts differ across captions; Appendix Table 4.2 says Mn in its caption but tabulates Co. Chapter 3 enrichment acetate wording differs from its medium table. The conclusion prints Mn(VI) where the chapter investigates Mn(IV). No corrected speciation series, growth-medium recipe or unique kinetic pathway is inferred from these discrepancies.
Context_only Source: ncbi_geobacter
NCBI 35554 resolves Geobacter sulfurreducens at species rank. It neither identifies the thesis's stock as strain PCA nor establishes mineral transformation by every member of this species.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Pyrochroite row PDF page 179 and feitknechtite row page 67; status and date definitions on pages 1-2.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14)
  2. buchanan_thesis: Buchanan, Dawn Melisa. The bioreduction of cobalt and nickel bearing manganese minerals. University of Manchester PhD thesis, cover dated 2021; repository award date 11 January 2022. Chapter 4, printed pages 115-158 (PDF pages 116-159), including Figures 4.1-4.8 and appendix figures/tables; Chapter 3 methods.
    https://pure.manchester.ac.uk/ws/portalfiles/portal/261215972/FULL_TEXT.PDF (accessed 2026-10-14)
  3. buchanan_repository: University of Manchester Research Explorer. Buchanan thesis metadata and original file; award date 11 January 2022. This is a thesis, not evidence of subsequent journal publication.
    https://research.manchester.ac.uk/en/studentTheses/the-bioreduction-of-cobalt-and-nickel-bearing-manganese-minerals/ (accessed 2026-10-14)
  4. ncbi_geobacter: NCBI Taxonomy 35554. Geobacter sulfurreducens, species rank; identity context only, not authentication of the unspecified Manchester laboratory stock.
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=35554&mode=Info (accessed 2026-10-14)
  5. post2023: Post, Heaney, Ilton and Elzinga (2023). The crystal structure of feitknechtite (beta-MnOOH) and a new MnOOH polymorph. American Mineralogist 108:2131-2141. Official accepted manuscript, structural Results/Discussion, Table 1 and Figures 1-3; identity context, not the Buchanan experiment.
    https://doi.org/10.2138/am-2022-8729 (accessed 2026-10-14)

Curation History

Timestamp Curator Action Summary
2026-10-14T09:18:34Z codex (GPT-6; codex) CREATE Added Feitknechtite identity and source-qualified culture-associated phase formation, preserving mixed solids, control limits, thesis status and unresolved spectral discrepancies.

Record source: data/records/feitknechtite.yaml