Montmorillonite mineral
Montmorillonite is a hydrated smectite mineral with generalized formula (Na,Ca)0.3(Al,Mg)2Si4O10(OH)2·nH2O, distinct from nontronite, generic smectite, mixed-layer illite-smectite and bentonite clay resources. The September 2026 IMA list retains the name as grandfathered, dated 1847; this date is not a numbered approval accession. The curated experiment used processed natural Source Clays SWy-2 rather than an ideal pure endmember. No criticality designation is inherited from aluminium, magnesium or other constituents.
Microbial & Biochemical Mechanisms (1)
Humic-associated enhancement of iron reduction in SWy-2 suspensions containing MR-1
redox transformation
Microbial
Associated Organisms:
Shewanella oneidensis MR-1 (NCBITaxon:211586)
Liu2017 observed increasing operational total iron(II) in montmorillonite SWy-2 suspensions containing washed Shewanella oneidensis MR-1 cells. Added humic acids increased iron(II) relative to live suspensions without added humic acid. The result supports a conditional culture-associated reduction phenotype and humic enhancement; it does not establish that every reduced iron atom came from the montmorillonite lattice, that the sterile controls for a different clay apply here, or that a dissolved iron product was recovered. The separate nontronite assays do not establish SWy-2 illite, silica or siderite production.
Experimental Context & Analytical Limits:
The source identifies SWy-2 from the Clay Minerals Society Source Clays Repository as montmorillonite and gives a structural composition, but does not provide a quantitative accessory-phase analysis of the experimental fraction. Bulk material was ground, soaked in 0.01 M NaCl for 24 hours, size-fractionated to 0.5–2.0 micrometres by centrifugation, washed until the AgNO3 chloride test was negative, freeze-dried and ground. MR-1, reported as ATCC 700550, was grown overnight in tryptic soy broth at 30 degrees C, harvested, washed and resuspended in sterile 10 mM PIPES, then held anaerobically. Basic assays used 50 mL serum bottles with 30 mL deoxygenated 10 mM PIPES, 0.03 g SWy-2, 3 mg KCl and 10–200 mg/L Aldrich, Suwannee River or Elliott soil humic acid, inoculated to approximately 10^8 cells/mL and shaken at 30 degrees C in darkness. Figure 1d–f spans up to 120 hours. The reduction-assay electron donor and PIPES pH are not explicitly stated in the inspected original or supplement; pH 7 used for a separate stock/model is not assigned to this assay. Figure 2b additionally labels 1, 5 and 10 g/L SWy-2 arms, although the Methods sentence introducing the expanded loading series names only NAu-2. This is laboratory iron redox chemistry, not demonstrated industrial extraction or microbial growth yield.
The source identifies SWy-2 from the Clay Minerals Society Source Clays Repository as montmorillonite and gives a structural composition, but does not provide a quantitative accessory-phase analysis of the experimental fraction. Bulk material was ground, soaked in 0.01 M NaCl for 24 hours, size-fractionated to 0.5–2.0 micrometres by centrifugation, washed until the AgNO3 chloride test was negative, freeze-dried and ground. MR-1, reported as ATCC 700550, was grown overnight in tryptic soy broth at 30 degrees C, harvested, washed and resuspended in sterile 10 mM PIPES, then held anaerobically. Basic assays used 50 mL serum bottles with 30 mL deoxygenated 10 mM PIPES, 0.03 g SWy-2, 3 mg KCl and 10–200 mg/L Aldrich, Suwannee River or Elliott soil humic acid, inoculated to approximately 10^8 cells/mL and shaken at 30 degrees C in darkness. Figure 1d–f spans up to 120 hours. The reduction-assay electron donor and PIPES pH are not explicitly stated in the inspected original or supplement; pH 7 used for a separate stock/model is not assigned to this assay. Figure 2b additionally labels 1, 5 and 10 g/L SWy-2 arms, although the Methods sentence introducing the expanded loading series names only NAu-2. This is laboratory iron redox chemistry, not demonstrated industrial extraction or microbial growth yield.
Curated Evidence Points:
Support
Source:
liu_2017
Figure 1d–f and Results pp.2–3 show total iron(II) time courses for SWy-2 with each humic-acid type and concentration, including live zero-humic-acid comparisons. Figure 2b separately varies SWy-2 loading with and without Elliott soil humic acid. Error bars represent SD for n=3; the Methods says experiments were performed at least three times. Total and dissolved iron(II) used the cited phenanthroline assay. These operational iron fractions are not synonymous with isolated dissolved-metal recovery or a phase-specific extraction mass balance.
Support
Source:
liu_2017_si
Figure S1c/d reports initial reduction rates and reduction extents for SWy-2. Figure S6 directly shows ethylene-glycolated SWy-2 XRD before exposure and after reduction without or with Elliott soil humic acid. Changes in diffraction support alteration of the processed clay, but neither a refined phase inventory nor complete conversion to a pure product is supplied. No numerical values were digitized from these plots.
Partial
Source:
liu_2017_si
The explicit sterile comparison in Figure S5b concerns NAu-2, not SWy-2. No matched sterile SWy-2 time course is presented in the inspected main or supplement. Zero-humic-acid SWy-2 arms still contain MR-1 and therefore are not abiotic controls. NAu-2-specific humic fractionation, electrochemical activity, Fe(II)-complexation experiments and dissolved-versus-solid-associated partitions cannot independently prove those mechanisms for SWy-2. Humic abiotic reducing capacity and accessory-iron contributions are not excluded by the accepted SWy-2 comparisons.
Partial
Source:
liu_2017
The detailed microscopy and assignments of illite, silica and tentative siderite in Figure 6 and supplementary Figures S7–S10 concern NAu-2. Their products and molecular interpretation are not transferred to this montmorillonite record. Added KCl also prevents interpreting any potassium in a possible product as wholly released from SWy-2. The two mineral records share this publication lineage and are not independent replication of one experiment.
Context_only
Source:
ncbi_mr1
Taxon 211586 resolves the named MR-1 strain. The taxonomy entry supports organism identity, not the mineral transformation or independent verification of the culture stock.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026; definitions pp.1–2 and Montmorillonite row PDF p.147, G, 1847, generalized formula. Retained official original re-inspected 14 October 2026.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14) -
montmorillonite_handbook: Handbook of Mineralogy: Montmorillonite, 2001 version 1.2; complete one-page entry, smectite-group membership, variable composition and identification caution. Original acquired and inspected 14 October 2026.
https://handbookofmineralogy.org/pdfs/montmorillonite.pdf (accessed 2026-10-14) -
liu_2017: Liu, G.; Qiu, S.; Liu, B.; Pu, Y.; Gao, Z.; Wang, J.; Jin, R.; Zhou, J. (2017). Microbial reduction of Fe(III)-bearing clay minerals in the presence of humic acids. Scientific Reports 7:45354. DOI 10.1038/srep45354. Complete nine-page original; SWy-2 Figure 1d–f, Figure 2b and Methods pp.7–8 re-inspected. Same study as the distinct NAu-2 nontronite record.
https://doi.org/10.1038/srep45354 (accessed 2026-10-14) -
liu_2017_si: Liu et al. (2017), original nineteen-page supplementary information srep45354-s1.pdf, acquired from the complete Europe PMC supplementary archive in round74 and re-inspected; SWy-2 Figures S1c/d and S6, and NAu-2-only scope of S2–S5 and S7–S10 checked.
https://www.ebi.ac.uk/europepmc/webservices/rest/PMC5371790/supplementaryFiles (accessed 2026-10-14) -
ncbi_mr1: NCBI Taxonomy: Shewanella oneidensis MR-1, taxon 211586, strain rank; current authoritative XML checked 14 October 2026.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=211586 (accessed 2026-10-14)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-14T15:42:02.178887+00:00 |
codex (GPT-6; codex) | CREATE | Created montmorillonite from the complete Liu2017 original and supplement, restricting microbial iron reduction to the distinct SWy-2 arms and preserving missing controls, donor/pH and product-transfer limits. |
Record source: data/records/montmorillonite.yaml