Mackinawite mineral
Mackinawite is the FeS mineral species listed as approved, with the designation 1967 s.p., in the September 2026 IMA compilation. The phase is distinct from unspecified iron monosulfide, pyrrhotite, greigite, pyrite and elemental iron. The evidence below concerns laboratory precipitation from dissolved reagents and direct crystallographic identification, not extraction from a natural mackinawite ore. No constituent-element criticality designation is inherited.
Microbial & Biochemical Mechanisms (1)
Mackinawite precipitation with sulfate-reducing AM13 and inactive-cell comparators
biomineralization
Microbial
Associated Organisms:
Maridesulfovibrio hydrothermalis AM13 = DSM 14728 (NCBITaxon:1121451)
Sulfide generated by live sulfate-reducing AM13 cultures reacted with supplied dissolved Fe(II), producing solids identified as mackinawite by powder X-ray diffraction. Mackinawite also formed in cell-free chemical controls. Crystalline domains were larger when live cells, or separately gamma-inactivated cells supplied with reagent sulfide, encountered Fe(II) before sulfide production or addition. The comparison supports an influence of microbial biomass on nucleation and growth, including a nonmetabolic contribution from inactive cells. It does not establish a specific enzyme, prove that microorganisms are necessary for mackinawite formation, or quantify recovery of a purified mineral product.
Experimental Context & Analytical Limits:
Picard et al. obtained Desulfovibrio hydrothermalis AM13 from DSMZ as DSM 14728; the verified strain node now uses Maridesulfovibrio. Washed stationary-phase cells were inoculated into an anoxic, bicarbonate-buffered marine medium containing sulfate and lactate, in 50 mL aliquots in 110 mL serum vials. FeCl2 supplied nominally 4 mM Fe(II), with measured mean 3.81 +/- 0.17 mM; initial pH was 7.03 and incubation was at 35 degrees C. Live-cell arms began at approximately 10^6 or 10^8 cells/mL. Cell-free arms received Na2S either as one addition or as daily additions over six days; a lactate-plus-acetate comparator was also tested. A separate arm received Fe(II) only after a live culture had already produced sulfide. Inactive-cell experiments used stationary-phase cells irradiated at 2 Gy/min for 48-72 hours, washed and resuspended in Fe medium; absence of sulfide production was the reported inactivation check. Those cells spent two weeks in Fe medium before reagent sulfide addition, a distinct pretreatment from the live-cell arm. Samples were prepared anaerobically for chemistry, diffraction and microscopy, with brief transfers to analytical instruments. Early phase comparisons used one week and two months; longer incubations extended to eleven months for live-cell experiments. Table 3 pools 10 live-cell, 5 inactive-cell, 11 abiotic and 5 post-growth Fe-addition results over unequal month ranges, rather than supplying those replicate counts at every time point. These are laboratory reagent-based mineralization experiments, not industrial deployment.
Picard et al. obtained Desulfovibrio hydrothermalis AM13 from DSMZ as DSM 14728; the verified strain node now uses Maridesulfovibrio. Washed stationary-phase cells were inoculated into an anoxic, bicarbonate-buffered marine medium containing sulfate and lactate, in 50 mL aliquots in 110 mL serum vials. FeCl2 supplied nominally 4 mM Fe(II), with measured mean 3.81 +/- 0.17 mM; initial pH was 7.03 and incubation was at 35 degrees C. Live-cell arms began at approximately 10^6 or 10^8 cells/mL. Cell-free arms received Na2S either as one addition or as daily additions over six days; a lactate-plus-acetate comparator was also tested. A separate arm received Fe(II) only after a live culture had already produced sulfide. Inactive-cell experiments used stationary-phase cells irradiated at 2 Gy/min for 48-72 hours, washed and resuspended in Fe medium; absence of sulfide production was the reported inactivation check. Those cells spent two weeks in Fe medium before reagent sulfide addition, a distinct pretreatment from the live-cell arm. Samples were prepared anaerobically for chemistry, diffraction and microscopy, with brief transfers to analytical instruments. Early phase comparisons used one week and two months; longer incubations extended to eleven months for live-cell experiments. Table 3 pools 10 live-cell, 5 inactive-cell, 11 abiotic and 5 post-growth Fe-addition results over unequal month ranges, rather than supplying those replicate counts at every time point. These are laboratory reagent-based mineralization experiments, not industrial deployment.
Curated Evidence Points:
Support
Source:
picard2018
Sections 2.1-2.5, Tables 1-2, Figures 1-2 and supplement S1-S2 distinguish the live, inactivated, cell-free and post-growth Fe-addition arms. Figure 2 assigns mackinawite reflections against the reference diffraction pattern in panel D; it is the only detected crystalline iron sulfide at one week and two months across these arms. Vivianite also occurs in inactive-cell and some abiotic samples, so the complete precipitate is not established as pure mackinawite. Identification rests on diffraction, not on the FeS formula or black precipitate color alone.
Support
Source:
picard2018
Section 3.2, Table 3 and Figure 3 show larger Scherrer-derived crystalline domains in live-cell and inactive-cell treatments than in cell-free and post-growth Fe-addition treatments. Figures 4-7 and S3 show differences in aggregation and cell-associated deposits. Crystalline-domain estimates, dynamic-light-scattering aggregate sizes and selected microscopy images measure different properties; none is a mineral recovery yield. The inactive-cell comparison supports a biomass contribution without implying sulfate reduction or other metabolism by killed cells.
Partial
Source:
picard2018
Table 2 and Figure S2 show that the controls approximate, rather than exactly match, sulfide exposure, Fe/S ratio and pH. Reported final pH values are about 7.06 for live Fe cultures, 7.30 for abiotic treatments and 7.37 for inactive-cell treatments. The inactive-cell pretreatment also permits vivianite formation before sulfide addition. Table 3 gives inactive-cell c-axis domain size as 18.5 +/- 7.7 nm, while Section 3.2 says 18.7 +/- 7.7 nm; no reconciled point estimate is adopted. The qualitative growth comparison is retained without claiming a completely isolated molecular cause or a universal biological size signature.
Partial
Source:
picard2018
Section 3.4 explicitly states that Fe/S elemental maps do not identify mineralogy at each cell surface. Assignment of those deposits to mackinawite is an inference from the bulk one-week diffraction result. Cell-surface binding and extracellular-polymer templating are proposed explanations, not results of purified-polymer or gene-disruption assays. The approximately 60% allocation of FeS to cell crusts in Sections 3.4 and 4.3 is a geometric estimate, not a measured recovered fraction.
Partial
Source:
picard2018
Figure 2C detects greigite alongside mackinawite in the five-month live treatment; Section 4.2 instead says greater than five months and reports residual mackinawite at eleven months. This is conditional phase evolution, not complete conversion or proof of enzymatic iron oxidation. Neither pyrite nor marcasite was detected in the tested samples. The null result is specific to these conditions, and Section 4.5 warns that reactant concentrations exceed those typical of natural sediments. No natural-feed extraction, field performance or isolated-metal recovery is demonstrated.
Context_only
Source:
ncbi_am13
The current strain node and source-name synonym resolve AM13 = DSM 14728 without assigning an unverified strain to a species-level experiment. Taxonomy verifies the label mapping, not the mineralization mechanism.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Mackinawite row, PDF page 130; column definitions and distribution terms on pages 1-2.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-11) -
picard2018: Picard, Gartman, Clarke and Girguis (2018). Sulfate-reducing bacteria influence the nucleation and growth of mackinawite and greigite. Geochimica et Cosmochimica Acta 220:367-384. Sections 2-4, Tables 1-3, Figures 1-7 and original supplementary Figures S1-S3.
https://doi.org/10.1016/j.gca.2017.10.006 (accessed 2026-10-11) -
ncbi_am13: NCBI Taxonomy 1121451. Maridesulfovibrio hydrothermalis AM13 = DSM 14728; source-name synonym Desulfovibrio hydrothermalis AM13 = DSM 14728.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=1121451&mode=Info (accessed 2026-10-11)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-11T21:09:39Z |
codex (GPT-6; codex) | CREATE | Added IMA-grounded mackinawite and AM13 mineralization evidence, distinguishing live-cell sulfate reduction, inactive biomass, chemical controls and conditional phase evolution, with source discrepancies and recovery limits retained. |
Record source: data/records/mackinawite.yaml