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Pyroaurite mineral

Pyroaurite is the magnesium-ferric-iron carbonate hydroxide hydrate mineral Mg6Fe3+2(OH)16(CO3)·4H2O. The IMA-CNMNC September 2026 list records redefined status Rd and the historical year 1865; that year is not a numbered approval identifier. It is distinct from hydrotalcite, the hydrotalcite mineral group, unspecified layered double hydroxides, elemental magnesium or iron, and mixed asbestos-mine tailings. The curated field trial identifies source-assigned pyroaurite in both inoculated and uninoculated acid-treated tailings and in the untreated baseline; it does not establish a microbial increase in pyroaurite production. No constituent criticality designation is inherited.

Microbial & Biochemical Mechanisms (1)

Pyroaurite occurrence during an inoculated tailings-carbonation field trial

other Microbial

Pyroaurite was assigned by powder X-ray diffraction and Rietveld analysis in mixed Woodsreef asbestos-mine tailings during a small field carbonation trial. An orange horizon appeared in both the chemically treated plot and the plot subsequently receiving a cyanobacteria-dominated consortium; pyroaurite was already present in untreated tailings. Microbial involvement here describes the deliberately inoculated experimental arm, not proof that the organisms formed this phase, increased its abundance, or were necessary for precipitation. The source proposes abiotic reprecipitation after acid treatment and carbon-limited phase selection; neither pathway was independently isolated. The reported biological benefit concerns hydromagnesite and is not transferred to pyroaurite.

Experimental Context & Analytical Limits:
Two unreplicated 1 m × 1 m × 0.5 m field plots at Woodsreef Mine, New South Wales, Australia, each received 40.5 L of 0.22 M sulfuric acid prepared in local creek water. After two weeks, the Bio-plot received 2 L of a consortium enriched from a local mine-pit biofilm plus 18 L of BG-11 medium made with creek water; the Chem-plot received 20 L of creek water without inoculum or BG-11. Thus liquid volume was matched but nutrients were not, and the open field comparator was not sterile. Both plots remained exposed for nine further weeks; adjacent unleached and uninoculated tailings supplied the mineralogical baseline. The consortium was not resolved to a verified strain or species, so none is assigned. Triplicate approximately 15 g samples at each depth were subsamples, not replicate treated plots. Baseline and two-week sampling combined 2–17 cm, whereas final sampling separated 2–4 and 4–17 cm. Samples were air-dried for two weeks, mixed with 10 wt% fluorite, ethanol-micronized, redried and analysed by powder XRD with source-defined Rietveld/Pawley fitting. The experimental mine-site setting is not evidence of commercial operation, net carbon-removal performance or isolated magnesium recovery.
Curated Evidence Points:
Sections 2.2–2.3, 3.1–3.3, Table 1 and Figures 2 and 5A–B support treatment, phase assignment and the mixed pyroaurite-bearing horizon. At final 2–4 cm depth, Table 1 reports 2.6 wt% pyroaurite in the Chem-plot and 2.5 wt% in the Bio-plot as average fitted phase proportions. Those values do not establish increased pyroaurite production or a recovered-product yield. The baseline already contained 1.3–2.6 wt% pyroaurite across its depth intervals, and acid treatment could dissolve pre-existing carbonate before reprecipitation. SEM platelets and orange colour are supporting morphology, not independent quantitative phase identification.
Tables S2–S5 retain individual fitted phase proportions and Rwp values. At final 2–4 cm, pyroaurite values are 2.6, 2.5 and 2.5 wt% in the uninoculated plot and 2.9, 3.2 and 1.3 wt% in the inoculated plot. These spatial subsamples are not independent plot-level biological replicates; no statistical inoculation effect or phase-specific mass balance is established. The acquired main article and supplement report the refinement results but do not display the underlying powder diffraction profiles, so the original pattern fits were not independently reproduced.
Section 4.2 warns that low-abundance phase uncertainty prevents straightforward comparison. Figure 7 is a calculated Mg-content normalization relative to serpentine, not an aqueous recovery measurement. Its graphical labels and caption identify A as Control, B as Chem-plot and C as Bio-plot, whereas the adjacent discussion reverses A and C; interpretation here follows the explicit table and graph labels. Section 3.2 also calls the two-week hydromagnesite interval 2–4 cm, while Methods, Table 1 and Table S3 use 2–17 cm. That depth-specific hydromagnesite comparison is not adopted as pyroaurite evidence.
Sections 3.1 and 4.3–4.5 and Figure 6 record no obvious surface carbonate crust or macroscopically visible field microbial growth at eleven weeks. Cyanobacteria could subsequently be cultured from Bio-plot material, with none recovered from Chem-plot material by that culture assay; this is not a census of all living microbes or a pyroaurite-specific causation test. Water infiltration, drying, heat and carbon supply were proposed limitations. Neither matched sterile, killed-inoculum nor nutrient-matched controls establish biological necessity. The more consolidated crust from the cited earlier laboratory study is a separate experiment, not this field result.
Figure S1 records nearby-town maximum temperature and precipitation over the experiment; Table S1 characterizes the creek water. Nutrient columns are labelled PO4-P, NO2-N and NO3-N, whereas the main narrative uses ion labels. No ionic-mass conversion, zero-for-nondetection substitution or new concentration observation is inferred from those differing labels.

Sources & References

  1. ima_202609: IMA-CNMNC master list, September 2026: definitions pp. 1–2 and Pyroaurite row p. 179
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14)
  2. handbook_pyroaurite: Handbook of Mineralogy: Pyroaurite; identity, formula and mineral association; version 1
    https://www.handbookofmineralogy.org/pdfs/pyroaurite.pdf (accessed 2026-10-14)
  3. mccutcheon_2017: McCutcheon, Turvey, Wilson, Hamilton and Southam (2017). Experimental Deployment of Microbial Mineral Carbonation at an Asbestos Mine: Potential Applications to Carbon Storage and Tailings Stabilization. Minerals 7(10):191. Complete 18-page published v2 PDF; Sections 2–4, Table 1 and Figures 1–7.
    https://doi.org/10.3390/min7100191 (accessed 2026-10-14)
  4. mccutcheon_2017_si: Original five-page supplement to McCutcheon et al. (2017): Figure S1 and Tables S1–S5. Same study, not independent replication.
    https://mdpi-res.com/d_attachment/minerals/minerals-07-00191/article_deploy/minerals-07-00191-s001.pdf (accessed 2026-10-14)

Curation History

Timestamp Curator Action Summary
2026-10-14T19:43:00.297803+00:00 codex (GPT-6; codex) CREATE Created a distinct carbonate hydroxide mineral owner from complete primary and authority evidence, retaining field-association, phase, control and source-consistency limits.

Record source: data/records/pyroaurite.yaml