Violarite mineral
Violarite is the cubic iron-nickel thiospinel mineral with ideal formula FeNi2S4. The September 2026 IMA list records grandfathered status and original-description year 1924, not a numbered approval. It is distinct from pentlandite, polydymite, greigite, elemental nickel and mixed ores. The accepted study uses violarite broadly for intermediate Fe–Ni thiospinel compositions rather than proving an ideal FeNi2S4 product. Its experiments were abiotic and do not inherit constituent criticality or demonstrate microbial production.
Microbial & Biochemical Mechanisms (1)
Abiotic hydrothermal replacement of pentlandite by a violarite-assigned phase
redox transformation
Controlled acidic hydrothermal treatment generated an XRD-assigned violarite component while pentlandite declined in mixed natural and synthetic feeds. Ex situ textures support a coupled dissolution–reprecipitation interpretation. These are laboratory chemical transformations, not microbial synthesis, a proven pure endmember or a closed nickel recovery process.
Experimental Context & Analytical Limits:
Tenailleau et al. (2006), p.707: one water-bath series used 1.0 g Mount Keith concentrate in 100 mL acetate-buffered solution at 80 degrees C and pH 3–5, approximately 0.2 molal total acetate. The concentrate was reported as 90 wt% pentlandite and 9 wt% pyrite with minor hydrotalcite/serpentine minerals and magnetite, below 0.1 mm. The design describes duplicate experiments at each pH, with Ar in one set and less than 0.05% H2S mixed into Ar in another; some reactions received 1 mL of 0.1 M ferric hydroxyacetate. Figure 1 compares two ferric-acetate arms at pH 3.4 differing in H2S addition. A separate hydrothermal series used 1–5 g synthetic pentlandite–pyrrhotite aggregates, approximately 1–2 mm, containing 39 wt% pentlandite and 61 wt% pyrrhotite. This feed was prepared by exsolution at 150 degrees C for 672 hours with natural pyrrhotite buffering. The cell operated at 120 degrees C and reported pressure 3.5 bar, with acetate solution circulated around the cell, daily solution replacement and sampling. Methods specify pH 4.0 while Figure 2 gives approximately 3.9. Removed samples dried on blotting paper at room temperature for 2–3 days before powder XRD/Rietveld analysis, with BSE imaging and EDS of polished products. No organism, biomass or inoculum was used.
Tenailleau et al. (2006), p.707: one water-bath series used 1.0 g Mount Keith concentrate in 100 mL acetate-buffered solution at 80 degrees C and pH 3–5, approximately 0.2 molal total acetate. The concentrate was reported as 90 wt% pentlandite and 9 wt% pyrite with minor hydrotalcite/serpentine minerals and magnetite, below 0.1 mm. The design describes duplicate experiments at each pH, with Ar in one set and less than 0.05% H2S mixed into Ar in another; some reactions received 1 mL of 0.1 M ferric hydroxyacetate. Figure 1 compares two ferric-acetate arms at pH 3.4 differing in H2S addition. A separate hydrothermal series used 1–5 g synthetic pentlandite–pyrrhotite aggregates, approximately 1–2 mm, containing 39 wt% pentlandite and 61 wt% pyrrhotite. This feed was prepared by exsolution at 150 degrees C for 672 hours with natural pyrrhotite buffering. The cell operated at 120 degrees C and reported pressure 3.5 bar, with acetate solution circulated around the cell, daily solution replacement and sampling. Methods specify pH 4.0 while Figure 2 gives approximately 3.9. Removed samples dried on blotting paper at room temperature for 2–3 days before powder XRD/Rietveld analysis, with BSE imaging and EDS of polished products. No organism, biomass or inoculum was used.
Curated Evidence Points:
Support
Source:
tenailleau2006
Figures 1–2 show declining pentlandite and increasing violarite-assigned phase fractions under the stated distinct conditions. Figure 3 shows progressive replacement of pentlandite lamellae, porous products and a narrow gap at the reaction front. These observations support the source's phase-assignment and replacement interpretation; the composition range called violarite is explicitly broader than the ideal mineral formula.
Partial
Source:
tenailleau2006
Results call the coarse hydrothermal experiments batch mode despite the flow-through apparatus description, and explicitly state that phase fractions are only semiquantitative because no independent phase standard was used. The abstract describes complete transformation after three days, but Figure 2 retains a nonzero refined pentlandite component and variable product fractions. Reported 80-degree conversion percentages are not adopted as closed nickel or whole-feed yields. Mixed feed, sampling, fluid replacement and secondary pyrite/marcasite formation prevent a simple one-phase mass balance.
Partial
Source:
tenailleau2006
Discussion p.708 states that EBSD did not establish the crystallographic relationship because the transformed violarite and surrounding pyrrhotite did not yield patterns; the abstract's broader characterization statement does not override that limitation. The authors also allow the apparent 200–400 nm reaction-front gap to have expanded during drying. Dissolution–reprecipitation is a supported textural interpretation, not directly observed in situ interfacial chemistry or proof of a unique microscopic pathway.
Context_only
Source:
tenailleau2006
Figure 4 is a thermodynamic calculation that excludes competing vaesite and polydymite; it is not a measured phase-boundary map or a comprehensive equilibrium test. The proposed 5–10 year natural transformation at 20 degrees C is an extrapolation, not an observed field time course. Potential flotation/smelting implications are motivation, not industrial deployment, isolated recovery or evidence for microbial necessity.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026; PDF page 229 Violarite row, pages 1–2 definitions and terms.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14) -
handbook: Handbook of Mineralogy. Violarite; one-page mineral description, cubic crystal data and FeNi2S4 composition.
https://handbookofmineralogy.org/pdfs/violarite.pdf (accessed 2026-10-14) -
tenailleau2006: Tenailleau, C., Pring, A., Etschmann, B., Brugger, J., Grguric, B. and Putnis, A. (2006). Transformation of pentlandite to violarite under mild hydrothermal conditions. American Mineralogist 91:706–709. DOI 10.2138/am.2006.2131; complete four-page letter, Methods, Results, Discussion and Figures 1–4.
https://doi.org/10.2138/am.2006.2131 (accessed 2026-10-14)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-14T14:44:37.481657+00:00 |
codex (GPT-6; codex) | CREATE | Created distinct violarite identity with qualified abiotic pentlandite replacement; retained broad product nomenclature, mixed feeds, semiquantitative XRD, unsuccessful EBSD and drying limits. |
Record source: data/records/violarite.yaml