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Acanthite mineral

Acanthite is the monoclinic silver sulfide mineral Ag2S, listed as grandfathered with original-description year 1855 in the September 2026 IMA master list. It is distinct from elemental silver, generic silver-containing nanoparticles and the high-temperature cubic Ag2S form commonly called argentite. A laboratory bacterial study identifies acanthite as a minority particle type within a mixed silver-containing population. No criticality designation is inherited from silver.

Microbial & Biochemical Mechanisms (1)

Minority acanthite particles associated with silver-exposed bacterial cells

biomineralization Microbial

Associated Organisms: Stutzerimonas stutzeri (NCBITaxon:316)

The strain reported as Pseudomonas stutzeri AG259 contained a small number of particles assigned to monoclinic Ag2S by combined electron diffraction and energy-dispersive X-ray analysis after growth on silver-nitrate-containing agar. Most of the analyzed silver was assigned to elemental silver, and a third crystal type remained unresolved. This supports culture-associated acanthite occurrence, without establishing an exclusively biological precipitation route, a pure product or a recovery yield.

Experimental Context & Analytical Limits:
AG259 was supplied by J. T. Trevors and described as originally isolated from a silver mine. The species mapping retains the authors' identification under the current NCBI name; no strain-specific accession or sequence is supplied in this study. Cultures were maintained in Lennox L broth and grown on Lennox L agar containing nominally 50 mM AgNO3 at 30 degrees C for 48 hours in the dark. The article does not specify assay pH, inoculum density, agar recipe, free dissolved silver concentration, biological replicate count or a matched cell-free, killed-cell or sulfide control series. Growing cells were harvested, fixed for two hours in 2.5% glutaraldehyde in distilled water, sedimented at 1500 g for ten minutes and washed three times. Thin-section preparation included ethanol dehydration, epoxy embedding and polymerization at 60 degrees C for two days; some sections were stained with uranyl acetate and lead citrate. TEM operated at 200 kV on titanium grids. The study is a laboratory microscopy observation in processed cells, not an ore-leaching assay, isolated silver-sulfide recovery or industrial deployment.
Curated Evidence Points:
Results and Discussion and Figure 3b identify a periplasmic particle type with an Ag-to-S atomic proportion of about 2 to 1 by EDX and diffraction spots assigned to the 030 and minus-1 minus-2 4 planes near the 401 zone axis of monoclinic acanthite. The authors report that the different crystal types were found in both whole cells and thin sections. Phase assignment uses diffraction together with composition; particle shape or nominal Ag2S composition alone is not the basis of this record. Figures 1 and 2 show cellular association and diverse particle morphologies, without assigning every visible particle to acanthite.
The paragraph describing Figure 3b calls the Ag2S particles a small number, without a counted fraction, bulk phase quantification, isolated product mass or silver mass balance. Figure 3a supports elemental Ag, whereas Figure 3c remains structurally unresolved despite an Ag-rich EDX spectrum. The reported overall particle size range is shared across crystal types and is not an acanthite-specific size distribution. The paper's introductory 25% dry-biomass silver figure comes from another study and is not a yield for AG259 in this experiment.
The proposed reaction of silver particles with bacterially produced H2S is an interpretation relying on an earlier reference; H2S production, its sulfur source and a causal enzymatic pathway are not measured here. Efflux and silver-binding explanations are also proposed. The absence of a matched chemical-control series and a native-state time course prevents isolating a biological increment or excluding effects of sample processing. Fixed-cell microscopy does not establish that inactive biomass alone produces acanthite. Prospective coating applications and preliminary mixed-particle coating observations do not demonstrate acanthite-specific functionality or industrial recovery.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. PDF page 3, Acanthite row; page 1 explains grandfathered status and original-description years. Retained original rechecked.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14)
  2. handbook_acanthite: Handbook of Mineralogy. Acanthite, version 1 (2001-2005), one-page species entry; monoclinic crystal data and distinction from high-temperature cubic argentite.
    https://handbookofmineralogy.org/pdfs/acanthite.pdf (accessed 2026-10-14)
  3. klaus1999: Klaus, Joerger, Olsson and Granqvist (1999). Silver-based crystalline nanoparticles, microbially fabricated. PNAS 96, 13611-13614. Complete original PMC full text, Materials and Methods, Results and Discussion, and original Figures 1-3, especially Figure 3b.
    https://doi.org/10.1073/pnas.96.24.13611 (accessed 2026-10-14)
  4. ncbi_stutzeri: NCBI Taxonomy 316. Stutzerimonas stutzeri, current species entry with Pseudomonas stutzeri as a homotypic synonym; not an identifier for strain AG259 or independent sequence verification of that historical isolate.
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=316&mode=Info (accessed 2026-10-14)

Curation History

Timestamp Curator Action Summary
2026-10-14T17:15:51Z codex (GPT-6; codex) CREATE Created phase-grounded acanthite record from the complete AG259 primary study, preserving mixed products, minority-phase scope, unresolved strain identity and missing causal controls.

Record source: data/records/acanthite.yaml