Maghemite mineral
Maghemite is the ferric iron oxide mineral commonly written gamma-Fe2O3, distinct from hematite, magnetite, elemental iron and an unresolved magnetic iron-oxide mixture. The September 2026 IMA list gives the vacancy-bearing formula (Fe3+0.67 vacancy0.33)Fe3+2O4 and status Rd, redefined through a 2018 special procedure; this is not an IMA proposal identifier. The curated laboratory study used synthesized nanomaghemite and supports culture-associated reduction toward magnetite-like products, with sulfate-dependent differences and mixed-product limitations. No iron criticality designation, natural-ore extraction yield or industrial deployment is inherited.
Microbial & Biochemical Mechanisms (1)
Culture-associated nanomaghemite reduction with and without added sulfate
redox transformation
Microbial
Associated Organisms:
Desulfovibrio sp. J01 (NCBITaxon:877574)
Gao et al. incubated a sulfate-reducing Desulfovibrio isolate with synthetic nanomaghemite in lactate media with or without added sulfate. Both inoculated treatments developed reduced Fe and magnetic and spectroscopic changes interpreted as transformation toward magnetite; the sulfate-containing treatment also developed sulfur-bearing secondary solids and a product closer to magnetite stoichiometry in the authors' fitted model. The paper cites HQ022824.1, which resolves to Desulfovibrio sp. J01; a named Desulfovibrio species is not assigned here. Direct cell-to-mineral electron transfer is a proposed explanation, not an experimentally isolated molecular pathway. The sulfate treatment can include indirect reaction with biologically produced sulfide.
Experimental Context & Analytical Limits:
Laboratory four-arm experiment M1-M4, with three parallel bottles per arm: M1 maghemite plus sulfate-free medium MA, M2 plus sulfate medium MB, M3 MA plus cells and M4 MB plus cells. The precursor was commercial goethite, reduced under H2 at 300 degrees C for 3.5 hours to nanomagnetite and then oxidized in air at 300 degrees C for three days. The starting maghemite had a reported Scherrer crystallite size of 28.1 nm and surface area 19.46 m2/g. Media were autoclaved at 121 degrees C for 30 minutes and mineral UV-treated for 40 minutes. Each nominal 30 mL serum bottle received 27 mL medium, 0.01 g ascorbic acid and 0.22 g mineral; the paper calls this 50 mmol/L but does not reconcile that concentration with the stated mass and final 30 mL volume, so no corrected loading is substituted. Cells from 3 mL culture were filtered and washed to remove residual sulfate and sulfide, then water brought the volume to 30 mL; the starting cell density is not reported. Preparation used an anoxic glovebox and N2:CO2 80:20 flushing, followed by shaking incubation at 37 degrees C for 31 days. Both media contained lactate, ammonium, phosphate and bicarbonate; MB contained Na2SO4 and MgSO4, with a reported medium sulfate concentration of 1.123 g/L before the stated dilution, while MA used chloride salts. Initial pH is not stated; endpoint pH was 7.46, 7.70, 7.19 and 7.33 in M1-M4. Solids were centrifuged, washed with anoxic water, freeze-dried and stored cold in anaerobic bags. No killed-cell, separated-cell, cell-free-metabolite or matched sulfide-only treatment isolates contact transfer. Ascorbate occurs in the sterile and inoculated arms; chloride and sulfate media are not identical in ionic composition. This is a synthetic-powder assay, not natural-ore processing or recovered iron.
Laboratory four-arm experiment M1-M4, with three parallel bottles per arm: M1 maghemite plus sulfate-free medium MA, M2 plus sulfate medium MB, M3 MA plus cells and M4 MB plus cells. The precursor was commercial goethite, reduced under H2 at 300 degrees C for 3.5 hours to nanomagnetite and then oxidized in air at 300 degrees C for three days. The starting maghemite had a reported Scherrer crystallite size of 28.1 nm and surface area 19.46 m2/g. Media were autoclaved at 121 degrees C for 30 minutes and mineral UV-treated for 40 minutes. Each nominal 30 mL serum bottle received 27 mL medium, 0.01 g ascorbic acid and 0.22 g mineral; the paper calls this 50 mmol/L but does not reconcile that concentration with the stated mass and final 30 mL volume, so no corrected loading is substituted. Cells from 3 mL culture were filtered and washed to remove residual sulfate and sulfide, then water brought the volume to 30 mL; the starting cell density is not reported. Preparation used an anoxic glovebox and N2:CO2 80:20 flushing, followed by shaking incubation at 37 degrees C for 31 days. Both media contained lactate, ammonium, phosphate and bicarbonate; MB contained Na2SO4 and MgSO4, with a reported medium sulfate concentration of 1.123 g/L before the stated dilution, while MA used chloride salts. Initial pH is not stated; endpoint pH was 7.46, 7.70, 7.19 and 7.33 in M1-M4. Solids were centrifuged, washed with anoxic water, freeze-dried and stored cold in anaerobic bags. No killed-cell, separated-cell, cell-free-metabolite or matched sulfide-only treatment isolates contact transfer. Ascorbate occurs in the sterile and inoculated arms; chloride and sulfate media are not identical in ionic composition. This is a synthetic-powder assay, not natural-ore processing or recovered iron.
Curated Evidence Points:
Support
Source:
gao2020
Sections 3.1-3.5, Tables 1-3 and Figures 1, 2, 4 and 5 support a culture-associated redox and structural change relative to the two uninoculated media controls. Controls retain approximately constant susceptibility and lack fitted surface Fe(II); inoculated solids develop Fe(II) XPS components, larger fitted lattice parameters and altered room-temperature Mossbauer spectra. Table 3 models M3 as cation-deficient and M4 as closer to magnetite stoichiometry. Figure 5 and Section 3.5 report susceptibility maxima at day 16 for M3 and day 11 for M4, followed by declines; neither inoculated curve had stabilized by day 31. These are magnetic observations, not transformation percentages or recovery yields.
Partial
Source:
gao2020
The mineral and causal assignments are qualified. Section 3.2 says no separate phase other than maghemite was resolved by XRD, then infers magnetite-like transformation from lattice shifts; overlapping nanophase diffraction alone does not establish a pure final phase. Mossbauer and XPS are fitted interpretations, and the sulfate arm contains additional paramagnetic and superparamagnetic components. Table 1 reports dissolved Fe(II) 0.822 mg/L and total dissolved Fe 1.032 mg/L only for M4; dashes for the other dissolved-Fe entries denote below detection, not zero, and numerical detection limits are absent. Solid Fe(II) wt% and fitted spectral areas are not purified-product yields. Sulfur XPS suggests sulfide species but does not uniquely identify mackinawite, greigite or pyrite as separate mineral products. Figure 3's English caption repeats Fe fitting labels from Figure 2, whereas its Chinese caption and body describe sulfur components; the sulfur interpretation is bounded to those labels and the actual plotted S spectrum. Table 3's doublet labels and areas are retained as source model assignments, not adopted as independently established phase fractions.
Partial
Source:
gao2020
Section 4 proposes direct transfer and more cell-mineral contacts when sulfate supports growth, but Figure 6 is a conceptual drawing, not microscopy or a contact-count experiment. Protein is used as a biomass proxy, with no initial growth series, contact exclusion or electron transfer mutant. Sulfide-mediated abiotic reaction, microbial metabolites and interaction with the added ascorbate are not separately apportioned. The stated triplicates have no displayed dispersion in the endpoint tables or susceptibility plot, limiting effect-size precision. Gao cites the same group's Zhou et al. 2019 work as prior work; that unavailable full study is not counted here as independent replication or used to import complete-conversion claims.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. PDF page 130, Maghemite row; page 1 status and special-procedure definitions. Previously acquired official PDF rechecked on the access date.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14) -
gao2020: Gao Y, Zhou Y, Xie Q, Chen T (2020). Effects of Sulfate on the Anaerobic Transformation of Maghemite-Magnetite. Geological Journal of China Universities 26(3):286-293. Chinese full text with English abstract; Sections 2-4, Tables 1-3 and Figures 1-6.
https://doi.org/10.16108/j.issn1006-7493.2019032 (accessed 2026-10-14) -
genbank_hq022824: GenBank HQ022824.1. Desulfovibrio sp. J01 16S ribosomal RNA gene, partial sequence, 1505 bp; source qualifier strain J01, sludge isolate, taxon 877574. Accession cited by Gao et al. Section 2.2.
https://www.ncbi.nlm.nih.gov/nuccore/HQ022824.1 (accessed 2026-10-14) -
ncbi_j01: NCBI Taxonomy 877574. Desulfovibrio sp. J01, species-rank entry within unclassified Desulfovibrio; does not establish a named species assignment.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=877574 (accessed 2026-10-14)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-14T10:43:58Z |
codex (GPT-6; codex) | CREATE | Created maghemite identity and a qualified primary Gao2020 culture-associated reduction mechanism, preserving strain resolution, control limitations, phase interpretation and source inconsistencies; Ohenhen supporting information and Zhou2019 full-text gaps remain separate research priorities. |
Record source: data/records/maghemite.yaml