CMMMech
CMMMech > Mineral > Ferrihydrite

Ferrihydrite mineral

Ferrihydrite is an approved mineral species in the September 2026 IMA list, with formula Fe(III)5O7(OH) and approval number 1971-015. The name also occurs in experimental descriptions of poorly crystalline synthetic two-line iron oxyhydroxides; that assay designation does not independently establish ideal IMA formula, natural origin or purity. This record concerns a characterized synthetic nanophase substrate, not iron metal, an ore grade or every Fe(III) oxide. The Ax17 assay is also represented under iron and the paired ferrihydrite/magnetite record; these are substrate/product perspectives on one experiment, not independent replication. No iron criticality designation is inherited.

Microbial & Biochemical Mechanisms (1)

Reduction of synthetic two-line ferrihydrite with secondary mineral formation

redox transformation Microbial

Associated Organisms: Desulfovulcanus ferrireducens (NCBITaxon:2831190)

Growing Desulfovulcanus ferrireducens Ax17 (DSM 111878) reduced synthetic two-line nanophase ferrihydrite and produced a black magnetic solid interpreted from complementary analyses as primarily cation-deficient magnetite. This is microbial Fe redox transformation with secondary mineral formation, not elemental iron production or a purified recovery product. The taxon identifier is species-level; the paper and DSMZ identify the experimental strain.

Experimental Context & Analytical Limits:
Laboratory triplicates used 50 mL modified DSM 981 medium in 160 mL serum bottles, reported 100 mmol/L ferrihydrite, initial pH 6.80 +/- 0.05, 0.5 mM cysteine-HCl, and 1.3 mM FeCl2 supplementation. The headspace was H2:CO2 (80:20) at 200 kPa; cultures received a 1% logarithmic-phase inoculum previously transferred at least three times on the acceptor, and grew at 55 degrees C for about five days. Identically composed uninoculated controls were incubated at 55 degrees C or room temperature. Ferrozine after oxalate dissolution gave reported Fe(II) of 24 mM in the biotic medium versus 2-3 mM in controls; this extraction-based measurement is not a dissolved-iron concentration or a recovery percentage. No pilot, industrial, or natural-ore extraction operation was tested. The source reports 84% retention of biogenic iron product in a separate pre-oxalate filtration comparison; this is an operational particulate fraction, not a magnetite phase percentage. No ideal starting ferrihydrite stoichiometry is inferred from the reported 100 mmol/L mineral addition.
Curated Evidence Points:
Methods and Results, Cell growth on ferrihydrite, link Ax17 growth, greater oxalate-extractable Fe(II), and the magnetic product to the inoculated treatment. Figures 1A, 2-4 and Supplementary Figures S2-S5 compare controls and mineral standards using reflectance, FTIR-ATR, Mossbauer spectroscopy, XRD, and TEM with electron diffraction.
This supports a magnetite-rich mixed product, not pure stoichiometric magnetite or uniquely biological magnetite formation. Low-temperature Mossbauer spectra exclude a pure magnetite product; XRD alone cannot distinguish magnetite, maghemite, and cation-deficient magnetite. The heated abiotic control formed lepidocrocite and may contain minor magnetite. Cysteine and added Fe(II) were present in all arms. Akaganeite and lepidocrocite treatments gave different, nonmagnetic poorly resolved products, limiting extrapolation across iron minerals.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. PDF page 69, Ferrihydrite row; page 1 column definitions and page 2 distribution terms.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-11)
  2. sklute2023: Sklute et al. (2023). Fe(III) (oxyhydr)oxide reduction by the thermophilic iron-reducing bacterium Desulfovulcanus ferrireducens. Frontiers in Microbiology 14:1272245. Methods, ferrihydrite Results, Figures 1-4, and Supplementary Figures S2-S5.
    https://doi.org/10.3389/fmicb.2023.1272245 (accessed 2026-10-11)
  3. ncbi_ferrireducens: NCBI Taxonomy 2831190 - Desulfovulcanus ferrireducens; species rank
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=2831190 (accessed 2026-10-11)

Curation History

Timestamp Curator Action Summary
2026-10-11T09:27:01.990810+00:00 codex (GPT-6; codex) CREATE Created ferrihydrite species identity with synthetic two-line substrate reduction and mixed-product limits.

Record source: data/records/ferrihydrite.yaml