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Pyrrhotite mineral

Pyrrhotite is the Fe7S8 mineral species listed in the September 2026 IMA compilation, with grandfathered status G and original-description year 1835. That year is not an IMA approval identifier. Experimental literature also uses the nonstoichiometric notation Fe1-xS; the principal study below characterized a monoclinic 4C specimen containing minor pyrite and marcasite. The species is distinct from iron, troilite, pentlandite and mixed sulfide ores or processing residues. No constituent-element criticality is inherited.

Microbial & Biochemical Mechanisms (1)

Culture-associated pyrrhotite oxidation and secondary iron mineral formation

bioleaching Microbial

In laboratory shake flasks inoculated with source-named Thiobacillus ferrooxidans strain TFI-35, pyrrhotite alteration advanced beyond chemical controls and produced elemental sulfur and secondary iron minerals. The initial acid-consuming stage resembled the chemical control; the later acid-producing stage accompanied greater mineral alteration. This supports conditional microbial participation in oxidative weathering, without establishing a dissolved-iron yield, isolated product or a uniquely demonstrated molecular pathway.

Experimental Context & Analytical Limits:
Bhatti et al. used a research-grade Santa Eulalia, Mexico specimen from Ward's Natural Science Establishment, number 49E5885, ground below 74 micrometres. XRD identified monoclinic 4C pyrrhotite with minor pyrite and marcasite. Living source-named T. ferrooxidans TFI-35 cultures were grown with 5% wt/vol pyrrhotite in a mineral salts solution containing 0.4 g/L each of ammonium sulfate, dipotassium hydrogen phosphate and magnesium sulfate heptahydrate in 0.005 M sulfuric acid. Shake flasks at 22 degrees C included chemical controls and sampling through 30 days. The paper does not specify flask volume, shaking speed, starting cell density or independent replicate counts. The historical organism name and strain label are retained without an inferred sequence or collection identifier. Residues were centrifuged, water-washed, air-dried and examined by XRD and SEM. Selective dissolution with acid ammonium oxalate or hydrochloric acid, followed by difference XRD, distinguished secondary phases. Dissolved iron was explicitly not analyzed.
Curated Evidence Points:
Pages 1985-1989 and Figures 1-6 show an early acid-consuming stage in both systems, then greater alteration in the inoculated system. Untreated material and day-30 chemical and inoculated residues were compared by XRD in Figure 2. Normalized pyrrhotite diffraction peaks were largely depleted by day 14; elemental sulfur appeared early, followed by K-jarosite, goethite and poorly crystalline schwertmannite identified with selective dissolution and difference XRD. Minor starting pyrite and marcasite persisted and became relatively enriched, rather than being demonstrated new products. These are laboratory solid-phase observations, not a mineral-to-metal recovery process.
Figure 3 normalizes selected diffraction peak intensities and does not measure absolute mineral mass fractions or a recovery percentage. The authors did not analyze dissolved iron and did not close a sulfur or iron mass balance. Chemical controls also altered the feed; the early pH/redox similarity argues against attributing every dissolution stage directly to cells. Coupled sulfur and iron oxidation and hydrolysis are the authors' interpretation; proposed transient sulfur oxyanions were not measured. SEM did not identify individual bacterial cells, so it does not demonstrate a contact mechanism. Replication, quantitative variability and transfer to an industrial system remain unestablished.
Context_only Source: kim2021
The 2021 study concerns a separate magnetically enriched fraction of Korean iron-mine waste containing pyrrhotite and quartz, with an indigenous enrichment rather than strain TFI-35. It reports 41-day aqueous iron results for adapted, nonadapted and abiotic arms at initial pH 2.8 and 3.2. Iron-bearing fresh medium and inoculum from iron-rich adaptation medium, without documented equivalent carryover blanks or corrections, prevent assigning all measured iron to the mineral or transferring a microbial increment to this mechanism. Table 1 fitted limiting concentrations are distinct from Figure 8 endpoint concentrations, although the abstract and conclusion blur that distinction. The methods' single-colony wording conflicts with Figure 4's multi-taxon profile. Missing strain accessions, leaching temperature, replicate counts and error-bar definitions further limit interpretation. This adjacent study does not establish recovered iron product, a quantified contact mechanism, or industrial deployment and is not pooled with the 1993 experiment.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. PDF page 180, Pyrrhotite row; pages 1-2, column definitions and distribution terms.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-11)
  2. bhatti1993: Bhatti, Bigham, Carlson and Tuovinen (1993). Mineral Products of Pyrrhotite Oxidation by Thiobacillus ferrooxidans. Applied and Environmental Microbiology 59(6):1984-1990. DOI 10.1128/aem.59.6.1984-1990.1993. Pages 1984-1989, experimental methods, Figures 1-6 and conclusions; PMCID PMC182203.
    https://doi.org/10.1128/aem.59.6.1984-1990.1993 (accessed 2026-10-11)
  3. kim2021: Kim, Koh and Kwon (2021). Bioleaching of Pyrrhotite with Bacterial Adaptation and Biological Oxidation for Iron Recovery. Metals 11(2):295. DOI 10.3390/met11020295. Sections 2-4, Figures 4 and 6-8, Table 1 and Equation 1.
    https://doi.org/10.3390/met11020295 (accessed 2026-10-11)

Curation History

Timestamp Curator Action Summary
2026-10-11T18:23:10.730452+00:00 codex (GPT-6; codex) CREATE Created IMA-grounded pyrrhotite identity with qualified laboratory weathering evidence and a separate, confounded iron-mobilization study retained as context.

Record source: data/records/pyrrhotite.yaml