Greigite mineral
Greigite is the mixed-valence iron sulfide mineral Fe2+Fe3+2S4, conventionally written Fe3S4, approved as IMA 1963-007 in the September 2026 IMA list. It is distinct from elemental iron, mackinawite, pyrite, magnetite, and an undifferentiated iron-sulfide precipitate. The observations below concern extracellular greigite formed in mixed laboratory mineral assemblages, not extracted natural ore or a purified recovered product. No criticality status is inferred from a constituent element.
Microbial & Biochemical Mechanisms (2)
Culture-associated extracellular greigite biomineralization
biomineralization
Microbial
Associated Organisms:
Thermococcus prieurii (NCBITaxon:1128108)
Thermococcus prieurii cultures produced extracellular greigite nanocrystals among pyrite-mineralized cells or vesicles and iron-phosphate-bearing organic material. Electron diffraction and high-resolution imaging support the Fe3S4 assignment. The authors propose nucleation on phosphate-loaded cell material; a unique molecular pathway, direct enzymatic Fe oxidation and an obligatory living-cell requirement are not established.
Experimental Context & Analytical Limits:
Early-stationary-phase cells, reported at 5 x 10^7 cells/mL, were incubated in anoxic mineralization medium containing 5 mM FeSO4 at 85 degrees C with shaking, sampled through 192 hours. Growth used modified Ravot medium adjusted to pH 7 before autoclaving, 1 g/L elemental sulfur, dinitrogen and 0.05% w/v Na2S.9H2O reductant. Phosphate was added to the growth medium, while the discussion calls some mineralization experiments nominally phosphate-free; transfer composition and phosphate carryover are not resolved. No measured mineralization pH trajectory, agitation speed or biological replicate count is provided. These are laboratory batch observations, not an in situ hydrothermal-vent demonstration or industrial recovery process.
Early-stationary-phase cells, reported at 5 x 10^7 cells/mL, were incubated in anoxic mineralization medium containing 5 mM FeSO4 at 85 degrees C with shaking, sampled through 192 hours. Growth used modified Ravot medium adjusted to pH 7 before autoclaving, 1 g/L elemental sulfur, dinitrogen and 0.05% w/v Na2S.9H2O reductant. Phosphate was added to the growth medium, while the discussion calls some mineralization experiments nominally phosphate-free; transfer composition and phosphate carryover are not resolved. No measured mineralization pH trajectory, agitation speed or biological replicate count is provided. These are laboratory batch observations, not an in situ hydrothermal-vent demonstration or industrial recovery process.
Curated Evidence Points:
Support
Source:
gorlas2018
Figures 1-2 and Results describe greigite appearing after 96 hours in T. prieurii incubations and becoming more abundant by 192 hours. More than 30 powder or single-crystal electron diffraction patterns were indexed as greigite rather than mackinawite, pyrrhotite or pyrite; Figure 2D shows a diffraction pattern and Figure 2E the lattice image. EDX Fe/S near 0.75 is complementary semiquantitative evidence, not sufficient phase identification alone. Particle and diffraction counts are not biological replicates. No greigite mass yield or iron-recovery fraction is measured.
Partial
Source:
gorlas2018
The paper reports that greigite was not observed in medium without cells. It does not provide a matched control phase-abundance time series or isolate effects of sulfide chemistry, cell debris and active metabolism. Figures 1 and 4 show a mixed assemblage containing separate pyrite spherules, greigite nanocrystals and organic material. The authors' description of locally pure greigite nanocrystals does not establish bulk phase purity. Close proximity to cells or vesicles is not intracellular magnetosome formation or demonstrated magnetic recovery.
Partial
Source:
gorlas2018
Figures 3-4 associate early amorphous iron-phosphate material with cells and extracellular material, followed by nearby greigite. This supports a proposed precursor association but does not prove an exclusive phosphate-to-greigite pathway. The Fe/P ratio alone does not measure Fe oxidation state, and the oxidant responsible for partial Fe(II) oxidation remains unresolved. S1-S2 are equilibrium model reports; the greigite model suppresses pyrite precipitation and is not an experimental control or evidence that greigite formation universally requires microorganisms.
Sulfur-source-dependent greigite formation in KOD1 cultures
biomineralization
Microbial
Associated Organisms:
Thermococcus kodakarensis KOD1 (NCBITaxon:69014)
In a separate study from the same research group, extracellular greigite was identified in Thermococcus kodakarensis KOD1 cultures grown with elemental sulfur or L-cystine and subsequently exposed to FeSO4. Elemental sulfur cultures developed a bulk greigite-pyrite assemblage, whereas L-cystine cultures contained sparse greigite nanocrystals in predominantly poorly ordered FeS. The two analytical scales and the distinct sulfur-source arms are retained; neither represents a purified greigite product.
Experimental Context & Analytical Limits:
KOD1 (JCM 12380) was grown to early stationary phase at a reported 5 x 10^7 cells/mL in modified Ravot medium containing yeast extract and tryptone, with either 1 g/L elemental sulfur or 1 g/L L-cystine. The medium was adjusted to pH 7 before autoclaving, supplemented with phosphate and 0.05% w/v Na2S.9H2O, and made anoxic using vacuum and dinitrogen. Addition of FeSO4 to a final 5 mM created the mineralization medium; cultures and cell-free controls were incubated at 85 degrees C with shaking. Main phase comparisons use microscopy at 144 hours and Fe K-edge XANES at 24 and 160 hours. Growth kinetics were in triplicate; the number of independent mineralization flasks or XANES biological replicates is not explicitly supplied. The methods give no agitation speed or mineralization pH trajectory.
KOD1 (JCM 12380) was grown to early stationary phase at a reported 5 x 10^7 cells/mL in modified Ravot medium containing yeast extract and tryptone, with either 1 g/L elemental sulfur or 1 g/L L-cystine. The medium was adjusted to pH 7 before autoclaving, supplemented with phosphate and 0.05% w/v Na2S.9H2O, and made anoxic using vacuum and dinitrogen. Addition of FeSO4 to a final 5 mM created the mineralization medium; cultures and cell-free controls were incubated at 85 degrees C with shaking. Main phase comparisons use microscopy at 144 hours and Fe K-edge XANES at 24 and 160 hours. Growth kinetics were in triplicate; the number of independent mineralization flasks or XANES biological replicates is not explicitly supplied. The methods give no agitation speed or mineralization pH trajectory.
Curated Evidence Points:
Support
Source:
gorlas2022
Figure 3D-F identifies extracellular L-cystine-arm nanocrystals as greigite by electron diffraction and high-resolution TEM at 144 hours. Figure 2 and Table 1 do not resolve greigite in the 160-hour bulk XANES fit for this arm, which is dominated by poorly ordered FeS and iron phosphates. The authors attribute the non-detection to low abundance, citing an approximate 5% XANES detection limit. Microscopic detection and bulk non-detection are not converted into contradictory presence claims or a quantified greigite yield. Pyrite was not observed in this arm.
Support
Source:
gorlas2022
For the elemental-sulfur arm, Figure 2D and Table 1 fit the 160-hour bulk Fe K-edge spectrum with greigite 41%, pyrite 49% and FeS 11%. These are fitted relative Fe-species contributions, sum to 101% as printed, and are not recovered masses, percentages of total culture solids or conversion of added iron. Supplementary Figures S2-S3 distinguish extracellular nanocrystals from pyrite-containing spherules. The article's Table 1 labels uncertainty intervals as 98% confidence, while the methods specify 99.7% (three sigma); the confidence convention is unresolved.
Partial
Source:
gorlas2022
Cell-free controls in both sulfur-source media are reported to contain amorphous FeS without observed greigite or pyrite. Supplementary Figure S6 directly illustrates a 70-hour elemental-sulfur control with SEM and EDX, not a complete phase-quantified control series matched to the 144-160-hour culture measurements. The comparisons support culture-associated formation under these conditions but do not isolate active metabolism from cell-derived substrates, templating and altered sulfur chemistry.
Partial
Source:
gorlas2022
Cell damage, iron-phosphate-rich debris and later greigite motivate the proposed precursor pathway. Dissolved phosphate release was explicitly not measured. ATP and cell-division observations in Figures 4-6 concern population response to mineralization and do not demonstrate that greigite alone causes survival or growth. Appendix S1 documents chemically synthesized XANES reference compounds, including greigite; these standards are distinct from the microbial assay products. No industrial deployment, isolated-product yield or universal biological origin of natural greigite is established.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. PDF page 86, Greigite 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) -
gorlas2018: Gorlas et al. (2018). Greigite nanocrystals produced by hyperthermophilic archaea of Thermococcales order. PLOS ONE 13(8), e0201549. Complete article, Figures 1-5 and original supplementary CHESS reports S1-S2.
https://doi.org/10.1371/journal.pone.0201549 (accessed 2026-10-11) -
gorlas2022: Gorlas et al. (2022). Precipitation of greigite and pyrite induced by Thermococcales - an advantage to live in Fe- and S-rich environments? Environmental Microbiology 24(2), 626-642. Complete archived article, Figures 1-6, Table 1, supplementary Figures S1-S8 and Appendix S1.
https://doi.org/10.1111/1462-2920.15915 (accessed 2026-10-11) -
ncbi_prieurii: NCBI Taxonomy 1128108. Thermococcus prieurii, species-level identity; the 2018 assay methods do not provide an authenticated strain accession.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=1128108 (accessed 2026-10-11) -
ncbi_kod1: NCBI Taxonomy 69014. Thermococcus kodakarensis KOD1, the strain named in the 2022 experimental methods as KOD1 (JCM 12380).
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=69014 (accessed 2026-10-11)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-11T21:09:26.932628+00:00 |
codex (GPT-6; codex) | CREATE | Created greigite identity and two bounded culture-associated biomineralization observations with mixed-phase, control, detection and laboratory-scale limitations; no recovery yield or criticality inferred. |
Record source: data/records/greigite.yaml