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Troilite mineral

Troilite is the FeS mineral species listed with grandfathered status G and original-description year 1863 in the September 2026 IMA compilation. That year is not an approval identifier. The hexagonal species is distinct from pyrrhotite, mackinawite, iron and mixed sulfide resources. The accepted laboratory study used a natural XRD-assigned troilite feed with marcasite impurity, not a demonstrated pure endmember. No constituent-element criticality is inherited.

Microbial & Biochemical Mechanisms (1)

Consortium-associated dissolution of troilite-bearing natural material

bioleaching Microbial

Living enrichments from two Copahue hot springs were associated with greater iron solubilization and loss of a troilite diffraction peak than an uninoculated control in laboratory shake flasks. Sulfur and iron oxidation, acidification and secondary iron precipitation were proposed explanations. The comparison supports conditional microbial participation in weathering of the characterized feed, without establishing a pure-phase dissolution rate, a specific organism's causal role or recovered iron product.

Experimental Context & Analytical Limits:
Baño 9 (B9) and Las Maquinitas (LM), Argentina, supplied unresolved natural communities enriched at 65 degrees C in M88 medium. B9 grew with sulfur or sucrose; LM grew with sulfur. FISH/CARD-FISH and microscopy provided partial community characterization, with predominantly archaeal signals, but no resolved strain identities or reliable population fractions. No isolate or sequence identifier is assigned. Natural mineral of unspecified collection provenance was milled below 74 micrometres; XRD identified troilite as the main component and marcasite as its main impurity. The feed was steam-sterilized by the procedure used for sulfur and added at a source-reported final concentration of 4%, whose mass/volume basis is not specified. Duplicate shake-flask experiments ran at 65 degrees C and 150 rpm for 70 days in nominally pH-2 M88 medium. Source-labelled inocula were B9+S, B9+Su and LM+S; the abiotic control replaced inoculum with fresh medium and is labelled Sterile+S in Figures 3-4. Flask and working volumes, inoculum volume, final cell loading and the exact equivalence of added nutrients versus inoculum carryover are unreported. Table 1 describes enrichment densities, not final reactor cell counts. Total soluble iron was measured by atomic absorption; water-washed, air-dried residues were assessed by XRD, selective dissolution and SEM.
Curated Evidence Points:
Section 3, printed pages 21-23 and Figure 3 report day-70 soluble iron as 60 plus or minus 12% for B9+S, 48 plus or minus 9% for LM+S, 32 plus or minus 7% for B9+Su and 15 plus or minus 2% for the abiotic control, relative to initial mineral-feed iron. These are the authors' reported percentages, not reconstructed values or isolated-product yields. Experiments were duplicated, but the meaning of the reported uncertainty is not defined. The appreciable sterile dissolution is retained; inoculation did not make all iron release biological.
Section 3, printed page 21 reports troilite dissolution estimates of 90.5%, 85.7%, 81.0% and 52.4% for B9+S, LM+S, B9+Su and control, respectively, from loss of the normalized 2.05-angstrom diffraction peak. These single-peak estimates are not refined phase mass fractions or the Figure 3 soluble-iron denominator. Figure 5 and Table 2 show residual troilite and marcasite together with secondary iron-bearing phases. Reprecipitation separates aqueous iron from apparent solid alteration. Initial quantitative phase purity and a closed iron/sulfur balance are unavailable; medium iron and inoculum carryover were not independently corrected in a documented source-resolved balance. No phase-specific metal recovery or product purification was demonstrated.
Methods 2.2/2.5 specify M88 medium prepared at pH 2 before mineral addition; Figure 4A plots early experimental-mixture values around 4.5-5 and the control near that range. Page 23 says the control maintained its initial pH but does not explicitly identify that value as 2. The preparation and reactor measurements have unresolved timing and material comparability. Acid-consuming dissolution after mineral addition could explain a rise, but paired pre/post-addition measurements are not reported, so neither that explanation nor a same-state pH contradiction is established. Separately, page 23 describes B9+S redox potential up to 600 mV while Figure 4B ends near 520 mV; that prose/graphic difference remains unresolved. The control was not matched to the evolving culture pH/redox, and no killed-cell comparison or isolated-member test separates direct contact from chemically mediated dissolution. Independent iron-oxidation assays are described as data not shown. Sulfur/iron oxidation and acid generation remain interpretations rather than a demonstrated molecular pathway or quantified taxon contribution.
Methods 2.4 and Table 2 support the authors' troilite assignment in a mixed natural feed. XRF values are reported as oxide equivalents, not identified oxide phases. The prose calls a particle's habit cubic despite the mineral's hexagonal identity; Figure 6 explicitly describes the residue particle as assumed troilite. Morphology and Fe/S composition alone do not establish the phase. Figures 1-2 characterize enrichment cells, not an independently demonstrated mineral-contact pathway. These laboratory results do not establish industrial performance.

Sources & References

  1. ima_2026_09: IMA-CNMNC (September 2026). The New IMA List of Minerals. PDF page 221, Troilite row; page 1, status and year definitions.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-15)
  2. handbook_troilite: Handbook of Mineralogy. Troilite, FeS. One-page entry, formula, hexagonal crystal system and natural occurrences.
    https://www.handbookofmineralogy.org/pdfs/troilite.pdf (accessed 2026-10-15)
  3. giaveno2011: Giaveno, Pettinari, Gonzalez Toril, Aguilera, Urbieta and Donati (2011). The influence of two thermophilic consortia on troilite (FeS) dissolution. Hydrometallurgy 106:19-25. DOI 10.1016/j.hydromet.2010.11.015. Sections 2.1-2.5 and 3, Tables 1-2 and Figures 1-6; complete original from CONICET, eight PDF pages including publisher cover.
    https://doi.org/10.1016/j.hydromet.2010.11.015 (accessed 2026-10-15)

Curation History

Timestamp Curator Action Summary
2026-10-15T06:12:07.652810+00:00 codex (GPT-6; codex) CREATE Created IMA-grounded troilite with qualified natural-feed bioleaching, preserved sterile dissolution and distinct soluble-iron versus diffraction estimates, and explicit source contradictions and controls.
2026-10-15T06:18:26.815090+00:00 codex (GPT-6; codex) EDIT Addressed independent F1 and issue 308 by distinguishing prepared-medium pH from reactor measurements and leaving post-addition acid consumption as an untested explanation; retained the separate redox discrepancy.

Record source: data/records/troilite.yaml