Diopside mineral
Diopside is the pyroxene mineral species CaMgSi2O6, listed as approved with the literal 1988 s.p. entry in the September 2026 IMA list. It is distinct from elemental magnesium or silicon, the pyroxene group, and mixed silicate rocks. The reviewed study used natural crystals with reported nonideal composition Ca0.99Mg0.98Fe0.02Cr0.01Si2O6 rather than an assumed pure synthetic end member. No constituent criticality designation is inherited.
Microbial & Biochemical Mechanisms (2)
Pseudomonas flow-through dissolution assay and proposed surface passivation
bioleaching
Microbial
Associated Organisms:
Pseudomonas reactans (NCBITaxon:117680)
Pseudomonas reactans exposure did not establish a consistent substantial increase in diopside constituent release relative to bacteria-free comparisons. Microscopy showed attached cells and biofilm-like coverage, and the authors proposed passivation from declining outlet concentrations. Baseline evolution and inconsistent source summaries prevent a universal inhibition factor or a demonstrated molecular passivation mechanism.
Experimental Context & Analytical Limits:
Natural ultrasonically cleaned 100-200 micrometre diopside (fresh BET area 1045 +/- 50 cm2/g) was tested in 25 mL stirred Teflon flow-through reactors at 25 +/- 0.5 degrees C and 0.018-0.022 mL/min. Stationary-phase cells were washed and starved for two days, then supplied at 0.54 or 3.85 g wet/L in 0.1 M NaCl with 10 mM MES or bicarbonate, with or without 10 percent nutrient broth. The sequence was bacteria-free, low biomass, high biomass, then bacteria-free again; successive stages used the same mineral. Table 1 reports pH 6.05-9.07 overall, including nutrient MES runs at 7.80-8.05 although Figure 2A groups them as pH about 6.1. Outlet samples passed 20-micrometre reactor filters and then 0.45-micrometre analytical filters; Ca/Mg used atomic absorption, Si molybdate-blue analysis. Rates were calculated from inlet-outlet concentration differences and fresh mineral surface area. No experimental strain accession is assigned beyond the source species name. Separate AFM cleavage-surface assays used about 1 g wet/L cells; their surface coverage is not a direct mass-balance assay.
Natural ultrasonically cleaned 100-200 micrometre diopside (fresh BET area 1045 +/- 50 cm2/g) was tested in 25 mL stirred Teflon flow-through reactors at 25 +/- 0.5 degrees C and 0.018-0.022 mL/min. Stationary-phase cells were washed and starved for two days, then supplied at 0.54 or 3.85 g wet/L in 0.1 M NaCl with 10 mM MES or bicarbonate, with or without 10 percent nutrient broth. The sequence was bacteria-free, low biomass, high biomass, then bacteria-free again; successive stages used the same mineral. Table 1 reports pH 6.05-9.07 overall, including nutrient MES runs at 7.80-8.05 although Figure 2A groups them as pH about 6.1. Outlet samples passed 20-micrometre reactor filters and then 0.45-micrometre analytical filters; Ca/Mg used atomic absorption, Si molybdate-blue analysis. Rates were calculated from inlet-outlet concentration differences and fresh mineral surface area. No experimental strain accession is assigned beyond the source species name. Separate AFM cleavage-surface assays used about 1 g wet/L cells; their surface coverage is not a direct mass-balance assay.
Curated Evidence Points:
Partial
Source:
pokrovsky2021
Results, Table 1 and Figures 1-2 support limited or unresolved enhancement under the tested conditions, with appreciable scatter. The source comparison is not uniformly pH matched: the nutrient MES rows are near pH 8 despite the pH 6 panel label. Its claim of a universal three- to five-fold start/end decrease also does not reconcile with Table 1 D3 and D4 endpoint rates. Figure 4 documents surface-associated material but does not identify an inhibitory molecule or prove that biofilm caused the rate changes. Methods give both 4-5 days for five reactor-volume renewals and a later 24 h steady-state statement; exact timing remains inconsistent. No rates, inhibition percentage or mineral-product recovery is adopted.
Partial
Source:
pokrovsky2021_si
Figure S1 shows time-dependent outlet Si concentrations through sequential bacterial and bacteria-free stages. Early declines and persistent changes are compatible with several causes; the sequence lacks a simultaneously aging bacteria-free reactor shown in this supplement. Its pH labels do not resolve the Table 1 discrepancy. These plots support documenting baseline drift and the authors' passivation proposal, not a uniquely demonstrated microbial cause or a uniform suppression factor.
Live and heat-killed fungal comparison with modest element-dependent effects
bioleaching
Microbial
The source-named Chaetomium brasiliense F-3649 produced slightly higher fitted silica-release rates than heat-killed biomass, without a matching magnesium increase and with variable calcium results. Fungal hyphae attached to mineral grains. The authors regarded the overall effect as weak or unresolved relative to their uncertainty; that does not erase the reported silica difference or surface changes.
Experimental Context & Analytical Limits:
Washed fungal biomass grown in Czapek medium was starved for two days; heat-killed biomass was autoclaved for one hour at 132 degrees C and washed. Six batch reactors comprised duplicate dead-biomass, live nutrient-free and live plus 1 percent Czapek-medium conditions. The dead arm did not have a corresponding nutrient-added treatment. The assay used 1.3 g of 100-200 micrometre natural diopside in 250 mL of 0.1 M NaCl at 25 +/- 1 degrees C, 120 rpm, for 19 days. Table 2 gives pH 6.13-6.50 and 4.46-5.6 g wet/L biomass; Methods and Figure S2 also mention 4.2 g wet/L, so an exact constant live/dead biomass match is not assumed. Ca/Mg/Si were measured in 0.45-micrometre filtrates. SEM solids were rinsed, freeze-dried and carbon coated. VKM corroborates the F-3649 name; no unverified current taxon or genome identifier is assigned.
Washed fungal biomass grown in Czapek medium was starved for two days; heat-killed biomass was autoclaved for one hour at 132 degrees C and washed. Six batch reactors comprised duplicate dead-biomass, live nutrient-free and live plus 1 percent Czapek-medium conditions. The dead arm did not have a corresponding nutrient-added treatment. The assay used 1.3 g of 100-200 micrometre natural diopside in 250 mL of 0.1 M NaCl at 25 +/- 1 degrees C, 120 rpm, for 19 days. Table 2 gives pH 6.13-6.50 and 4.46-5.6 g wet/L biomass; Methods and Figure S2 also mention 4.2 g wet/L, so an exact constant live/dead biomass match is not assumed. Ca/Mg/Si were measured in 0.45-micrometre filtrates. SEM solids were rinsed, freeze-dried and carbon coated. VKM corroborates the F-3649 name; no unverified current taxon or genome identifier is assigned.
Curated Evidence Points:
Partial
Source:
pokrovsky2021
Table 2 and Figure 3 show the modest, element-dependent live/dead differences and duplicate-reactor variation. The source reports higher live-fungus silica rates yet concludes effects are weak at its stated uncertainty; no uniform null or robust enhancement factor is substituted. Figure 5 and Results describe rounded or etched grain edges, but Discussion later broadly says no dissolution sites; panel a is described as dead-fungus material in Results and sterile/no-fungus in the caption and image. Therefore microscopy is used for attachment and qualified surface-alteration context, not definitive causal control evidence. No isolated Ca, Mg or Si product, field rate or industrial recovery is demonstrated.
Partial
Source:
pokrovsky2021_si
Figure S2 illustrates rising dissolved silica in one example from each fungal treatment. It is not a raw replicate dataset, and plotted biomass labels differ slightly from Table 2. The supplement supports the time-course context but does not resolve treatment comparability or source inconsistencies.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026; definitions PDF pages 1-2, Diopside row page 57 and Wollastonite row page 235.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14) -
handbook: Handbook of Mineralogy. Diopside, version 1.2 (2001), one-page entry; mineral identity and pyroxene-group context.
https://www.handbookofmineralogy.org/pdfs/diopside.pdf (accessed 2026-10-14) -
pokrovsky2021: Pokrovsky et al. (2021). Weak impact of microorganisms on Ca, Mg-bearing silicate weathering. npj Materials Degradation 5:51. DOI 10.1038/s41529-021-00199-w; complete ten-page article, Tables 1-2 and Figures 1-5.
https://doi.org/10.1038/s41529-021-00199-w (accessed 2026-10-14) -
pokrovsky2021_si: Supplementary Information to Pokrovsky et al. (2021), DOI 10.1038/s41529-021-00199-w; two pages, Figures S1-S2; publisher-linked file 41529_2021_199_MOESM1_ESM.pdf.
https://media.springernature.com/original/springer-static/esm/art%3A10.1038%2Fs41529-021-00199-w/MediaObjects/41529_2021_199_MOESM1_ESM.pdf (accessed 2026-10-14) -
ncbi_reactans: NCBI Taxonomy 117680, Pseudomonas reactans, species; official XML checked 14 October 2026. This is name-level grounding, not authentication of the experimental strain.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=117680&mode=Info (accessed 2026-10-14) -
vkm_f3649: All-Russian Collection of Microorganisms (VKM), fungal catalogue, Chaetomium brasiliense F-3649 entry; checked 14 October 2026. Catalogue corroborates the collection code, not the experimental culture identity or activity.
https://vkm.ru/rus/catalog/list/fungi.htm (accessed 2026-10-14)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-14T10:05:32.176696+00:00 |
codex (GPT-6; codex) | CREATE | Created mineral record from controlled primary microbial dissolution studies, retaining null/limited outcomes, source inconsistencies and limits on causal and field extrapolation. |
Record source: data/records/diopside.yaml