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Vermiculite mineral group

Vermiculite denotes compositionally variable hydrated layer silicates, represented here at mineral-group scope rather than as a particular ideal endmember or traded exfoliated product. The Handbook of Mineralogy explicitly calls vermiculite a group name with unspecified individual minerals; the September 2026 IMA list also retains Vermiculite as a grandfathered name, dated 1824, with generalized formula Mg0.7(Mg,Fe,Al)6(Si,Al)8O20(OH)4·8H2O. These nomenclature treatments are both retained. The experiment below concerns one characterized natural specimen deliberately exchanged with potassium before fungal exposure, not all vermiculite ores or naturally potassium-rich material. No constituent criticality designation is inherited.

Microbial & Biochemical Mechanisms (1)

Fungal-associated potassium acquisition and alteration of potassium-exchanged vermiculite

bioleaching Microbial

Associated Organisms: Paxillus involutus (NCBITaxon:71150)

Paxillus involutus grown with potassium-exchanged vermiculite had greater potassium concentration in harvested mycelium than the potassium-depleted mineral-free fungal control, and the exposed flakes showed surface furrows, localized erosion and adhering hyphae. This supports conditional fungal-associated potassium acquisition and surface alteration. It does not establish how much potassium release was uniquely caused by the fungus, distinguish abiotic cation exchange from biological enhancement, or quantify recovery of an isolated potassium product.

Experimental Context & Analytical Limits:
Pinzari2024 used the source-reported ATCC 200175 strain, whose ITS identity-checking procedure is described in SI S2. The natural vermiculite was NHM specimen BM 1941,89, reported as collected north of Loole Kop, Palaboroa, Pietersburg, Transvaal. SI S3 gives SEM-EDX/microprobe composition and reports no other minerals detected by XRD, without a quantitative trace-phase detection limit. Potassium exchange used KCl at 4.42 g per 100 mL for 14 days under agitation; this deliberate loading is distinct from native mineral potassium. Flakes of approximately 2 cm2 were ultrasonically cleaned in deionized water and autoclaved at 121 degrees C for 15 minutes. Each 100-by-20 mm Petri dish contained 30 mL modified Melin–Norkrans agar, a sterile cellophane membrane and mineral flakes, with three 5 mm plugs from seven-day cultures. Incubation was 21 days at 25 degrees C in darkness. The mineral and negative-control arms omitted KH2PO4; ammonium phosphate was adjusted to balance phosphorus against complete-medium positive controls, not to establish identical nitrogen conditions. Agar and cellophane retained potassium, so depleted does not mean potassium-free. Five biological replicates per condition supplied elemental and biomass measurements. This plant-free laboratory assay is not an industrial process or demonstrated transfer of mineral nutrients to a plant.
Curated Evidence Points:
Table 3 reports potassium at 25.11 ± 4.31 micrograms per gram dry mycelium for K-vermiculite, versus 5.52 ± 1.69 in the depleted control and 304.11 ± 11.05 in the complete-medium control (means ± SD, n=5). Their distinct statistical groups b, c and a support the reported ANOVA/Tukey contrast. Methods 2.3 removed mineral flakes before digestion, but these harvested-material concentrations are not a mineral-release fraction or total recovered potassium; microscopic carryover and intracellular versus surface-associated potassium were not separately resolved. Figure 1c1–c3 compares initial and fungus-exposed flakes and shows the surface changes.
Methods S1–S3 and Figure S1 establish distinct mineral and fungal-control arms, the strain-identification procedure, specimen provenance, KCl pretreatment and preparation. SI S3 assigns the exchanged material structural formula (Si2.96Al0.81Fe3+0.23)(Mg2.86Fe3+0.09Ti0.05Cr0.01)(Mg0.23Ca0.01K0.38)O10(OH)2, with tetrahedral, octahedral and interlayer groups, respectively. This specimen-specific formula does not define every member of the vermiculite grouping.
The five-condition experiment has fungal mineral-free positive/negative controls but no reported matched aged fungus-free K-vermiculite arm. Before-exposure images do not supply that control. Abiotic release of the deliberately exchanged potassium and dissolution caused by acidified medium therefore remain alternatives to a uniquely fungal extraction contribution. Table 1 gives initial pH 5.6 ± 0.1 and final vermiculite-arm pH 2.27 ± 0.33; its statistical group overlaps the depleted control. Table 2 also gives overlapping dry-biomass groups for vermiculite and both controls, so increased potassium concentration is not proof of increased dry biomass.
Discussion 4.1 says aluminium in vermiculite-grown mycelium was significantly greater than in controls, but Table 3 assigns vermiculite and both controls the same aluminium group b. No significant aluminium-acquisition claim is accepted here. Figures 2–5, Table 5 and Discussion 4.2 show expression responses, but no knockout or enzyme-specific intervention demonstrates the proposed exchange, physical-pressure or redox pathways. The paper reports no significant upregulation of its identified potassium-transporter genes versus the depleted control. Related Pinzari2022 work is not counted as an independently verified replication.
Context_only Source: ncbi_paxillus
Current taxon 71150 establishes the species name. ATCC 200175 remains the strain reported by the original paper, not an independently authenticated culture stock or strain-specific NCBI identifier.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026; definitions pp.1–2 and Vermiculite row PDF p.228, G, 1824, generalized formula. Retained official original re-inspected 14 October 2026; the date is not a numbered approval accession.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14)
  2. vermiculite_handbook: Handbook of Mineralogy: Vermiculite, 2001 version 1.2; complete one-page entry, especially Mineral Group field explicitly describing a group name. Original acquired and inspected 14 October 2026.
    https://handbookofmineralogy.org/pdfs/vermiculite.pdf (accessed 2026-10-14)
  3. pinzari_2024: Pinzari, F.; Cuadros, J.; Saiardi, A.; Humphreys-Williams, E.; Jungblut, A.D. (2024). Bespoke strategies of Paxillus involutus to extract potassium from diverse phyllosilicates. Fungal Biology 128:2341–2354. DOI 10.1016/j.funbio.2024.08.002. Complete fourteen-page original re-inspected, especially Methods 2.1–2.3, Tables 1–3 and Figure 1c. Same publication as the separate muscovite record, not an independent study.
    https://doi.org/10.1016/j.funbio.2024.08.002 (accessed 2026-10-14)
  4. pinzari_2024_si: Pinzari et al. (2024) official supplementary material, original DOCX mmc1; complete Methods S1–S3 and Figures S1–S2 inspected through original text and all five rendered pages. KCl exchange and BM 1941,89 specimen apply to the vermiculite arm.
    https://ars.els-cdn.com/content/image/1-s2.0-S1878614624001065-mmc1.docx (accessed 2026-10-14)
  5. ncbi_paxillus: NCBI Taxonomy: Paxillus involutus, taxon 71150, species rank; current authoritative XML checked 14 October 2026. This is not a strain-specific accession.
    https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=71150 (accessed 2026-10-14)

Curation History

Timestamp Curator Action Summary
2026-10-14T15:42:02.162672+00:00 codex (GPT-6; codex) CREATE Created group-scoped vermiculite from the complete Pinzari2024 original and official supplement, retaining K exchange, elemental-assay controls, source statistical conflict and laboratory limits.

Record source: data/records/vermiculite.yaml