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Chromite mineral

Chromite is the Fe(II)Cr2O4 mineral species, grandfathered in the September 2026 IMA list with original-description year 1845. It is distinct from elemental chromium, chromate, chromium-bearing spinels of unspecified composition, mixed chromite ores and processing tailings. The natural specimen called chromite in the experiment below was not compositionally or crystallographically characterized in that paper. Its measured Fe(II) change is a specimen-associated observation, not proof of conversion of pure endmember chromite. No criticality designation is inherited from chromium.

Microbial & Biochemical Mechanisms (1)

Anoxic cell-associated oxidation of assay-accessible Fe(II)

redox transformation Microbial

Associated Organisms: Azospira oryzae PS (NCBITaxon:640081)

The source reports Fe(II) oxidation in natural source-labelled chromite incubated with anoxic washed whole-cell suspensions of Dechlorosoma suillum strain PS, coupled to nitrate reduction. The organism identifier uses NCBI's current strain label; it does not imply genomic authentication of the experimental stock. Neither chromium oxidation state nor chromium release was measured in this assay.

Experimental Context & Analytical Limits:
Laboratory mineral-screening assay. Table 1 reports 9.42 mmol Fe(II) oxidized per kg mineral and 95.00% of the starting Fe(II). The footnote defines Fe(II) determination by ferrozine after 6 N HCl treatment over 24 h; these are operational extraction-based quantities, not a chromite dissolution percentage, total chromium conversion or recovery yield. Specimen origin, purity, grain size, mineral and cell loadings, nitrate concentration, pH, temperature, incubation time and replicate/error information for the chromite arm are not reported. Conditions from the separate FeCl2 and almandine experiments are not assigned to chromite. The study does not demonstrate an extraction process, isolated recovery product or industrial deployment.
Curated Evidence Points:
Table 1 on page 2847 supplies the chromite-specific assay values, nitrate coupling, washed-cell state and acid/ferrozine analytical method. Its associated paragraph reports no Fe(II) oxidation in abiotic controls or without a suitable electron acceptor, but supplies no chromite-specific control values or time course.
The Fe(II) assay does not resolve lattice iron from accessory or surface-associated iron and does not quantify chromium. Direct enzymatic attack on chromite and the relative contribution of secondary chemical reactions are unresolved. Figure 4 follows almandine, not chromite. The magnetite-containing mixed product in Figure 3 was formed in separate FeCl2 experiments; the paper also allows an abiotic green-rust/nitrate step there. No chromite-to-magnetite product is established.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. PDF page 45, Chromite 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. chaudhuri2001: Chaudhuri, Lack and Coates (2001). Biogenic Magnetite Formation through Anaerobic Biooxidation of Fe(II). Applied and Environmental Microbiology 67(6), 2844-2848. Table 1 and associated paragraph on page 2847; Figures 1-4 distinguish soluble-iron, product and almandine experiments from the chromite assay.
    https://doi.org/10.1128/AEM.67.6.2844-2848.2001 (accessed 2026-10-11)
  3. ncbi_ps: NCBI Taxonomy 640081. Current label Azospira oryzae PS; Dechlorosoma suillum PS is a listed heterotypic synonym; no-rank strain entry.
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=640081 (accessed 2026-10-11)

Curation History

Timestamp Curator Action Summary
2026-10-11T18:25:10.652259+00:00 codex (GPT-6; codex) CREATE Created chromite species identity with a qualified specimen-associated Fe(II) oxidation observation and explicit analytical, control and mineral-specific limits.

Record source: data/records/chromite.yaml