Bixbyite-(Mn) mineral
Bixbyite-(Mn) is the Mn(III)-dominant member of the bixbyite series, with ideal formula Mn2O3 under IMA-CNMNC decision 21-H. It is listed as redefined by a 2021 special procedure in the September 2026 list. It is distinct from the Fe-dominant species bixbyite-(Fe), the broader bixbyite structural series, elemental manganese and MnO2 minerals. The laboratory culture product below was assigned only as bixbyite-like Mn oxide by its authors. Its placement here expresses the Mn-rich structural analogy, not a retrospective certification of pure natural bixbyite-(Mn). No criticality designation is inherited from manganese.
Microbial & Biochemical Mechanisms (1)
Acidic T-G1 culture-associated formation of a bixbyite-like manganese oxide
biomineralization
Microbial
Associated Organisms:
Mesorhizobium australicum (NCBITaxon:536018)
Laboratory cultures of isolate T-G1 oxidized added dissolved Mn(II) and accumulated Mn-rich particles at pH 5.5. Raman and diffraction results were interpreted as a bixbyite-like phase associated with bacterial cells. The phase assignment remains qualified: it is not a refined pure-mineral composition, quantified phase fraction or demonstrated natural occurrence. Related oxidation and protein assays suggest enzyme involvement, but no purified enzyme or genetic intervention establishes a unique mineral-forming pathway. Neither isolated manganese recovery nor industrial treatment was demonstrated.
Experimental Context & Analytical Limits:
Bohu2015 isolated T-G1 from a Mn-rich layer 70 cm beneath a former uranium-leaching heap at Ronneburg, Germany, sampled in November 2011. Its 16S sequence was reported 99% similar to M. australicum WSM2073; the experimental isolate is not that type strain. Formation experiments used liquid peptone/yeast extract/glucose medium with 0.1, 1 or 10 mM MnSO4, buffered to pH 5.5 with 10 mM MES, incubated at 15 degrees C in darkness without shaking. The paper describes visible liquid-culture oxidation after several months and no pH change after 90 days, but does not unambiguously map the Figure 3 phase analyses to a specific Mn loading, exact harvest age or vessel gas exchange. The separate approximately eight-day microplate oxidation assay used 100 micromol/L MnSO4, pH 5.5 or 7.2 and three biological replicates; it is not a mineral-production time course or mass balance.
Bohu2015 isolated T-G1 from a Mn-rich layer 70 cm beneath a former uranium-leaching heap at Ronneburg, Germany, sampled in November 2011. Its 16S sequence was reported 99% similar to M. australicum WSM2073; the experimental isolate is not that type strain. Formation experiments used liquid peptone/yeast extract/glucose medium with 0.1, 1 or 10 mM MnSO4, buffered to pH 5.5 with 10 mM MES, incubated at 15 degrees C in darkness without shaking. The paper describes visible liquid-culture oxidation after several months and no pH change after 90 days, but does not unambiguously map the Figure 3 phase analyses to a specific Mn loading, exact harvest age or vessel gas exchange. The separate approximately eight-day microplate oxidation assay used 100 micromol/L MnSO4, pH 5.5 or 7.2 and three biological replicates; it is not a mineral-production time course or mass balance.
Curated Evidence Points:
Partial
Source:
bohu2015
Figure 3 and Results on page 6 show cell-associated micron-scale aggregates, Mn/O-rich EDS spectra, tentative Raman assignment and an XRD pattern compared with bixbyite reference peaks. The Raman bands at 337, 489 and 698 cm-1 differ from cited reference positions; carotenoid bands and additional elements are also present. The source attributes those differences to possible incorporation of other elements, but qualitative EDS does not establish lattice substitution. Small associated nanoparticles were not characterized. No Rietveld refinement, complete compositional assay, quantitative phase purity or direct bulk Mn-valence determination is reported.
Partial
Source:
bohu2015
Methods on page 3 use centrifuged, air-dried precipitate for Mo-Kalpha XRD and direct particles from liquid culture for Raman. SEM material was fixed in pH 7.4 phosphate-buffered saline, washed, ethanol-dehydrated and air-dried; hydrated unpreserved CLSM is a different preparation. The paper does not provide a matched uninoculated long-incubation XRD/Raman series or an in situ phase time course. Culture association and source-assigned phase formation are supported, but exclusive microbial necessity, a primary versus secondary transformation route and absence of preparation effects remain unresolved. Figure 1's no-Mn culture is a substrate-omission comparison, not a sterile Mn-containing formation control.
Support
Source:
bohu2015
Figure 4 shows increasing LBB-reactive Mn(III/IV) signal with culture growth at pH 5.5 and a larger but transient signal at pH 7.2, alongside a low plotted control. Its caption says the two pH control series overlap; their full preparation is not specified separately enough to convert this into a long-term mineral-phase control. LBB reports oxidizing equivalents calibrated with KMnO4, not a bixbyite-specific concentration. The discussion explicitly reports no solid Mn-oxide particles in the pH 7.2 liquid cultures despite positive LBB and Mn(III)-trapping assays. Oxidation therefore does not imply mineral precipitation or recovery under both conditions.
Partial
Source:
bohu2015
Figures 5-7 relate cell-free Mn(III) trapping, protein activity and transcript/protein assays to pH. Proteinase K suppresses the pH 5.5 trapping signal; SOD does not significantly change it in the reported comparison. Laccase-like activity and a targeted transcript were associated with acidic cultures, whereas superoxide production was higher in stationary cultures at pH 7.2. These interventions and associations concern oxidation assays, not an isolated demonstration that a named enzyme makes the Figure 3 mineral. No mutant rescue, purified enzyme product or unique causal gene is established. Figure 6's blue gel coloration is explicitly an image-processing choice by the authors; it is not an independently observed pigment.
Partial
Source:
bohu2015
Methods specify 100 micromol/L MnSO4 and pH 5.5/7.2 for growth comparisons, while the discussion refers to 500 micromol/L and pH 5.5/6.8. The ABTS assay text states 0.5 mM but its printed 300 microlitres of 15 mM substrate in 3 mL implies a different nominal concentration. These unresolved recipe discrepancies are not harmonized or used for quantitative comparisons. No kinetic rate, enzyme-normalized effect or recovery percentage is adopted.
Context_only
Source:
bohu2015
Supplementary Table S1 describes source soil and porewater chemistry, with the porewater values reused from Burkhardt2009. It contains no laboratory mineral yield, field deployment or new bixbyite recovery dataset. The paper describes the source layer as bearing birnessite and todorokite from earlier work; the laboratory product is not proof that bixbyite-(Mn) formed or predominates at that field site.
Context_only
Source:
cnmnc21h
Decision 21-H defines bixbyite as a series and bixbyite-(Mn) as its Mn3+-dominant member, including the orthorhombic Mn2O3 polytype. This grounds the modern record identity without upgrading the 2015 culture product's qualified phase assignment or assigning it to a specific polytype.
Context_only
Source:
ena_tg1
The accession identifies the submitted partial 16S sequence as T-G1 and cross-references this paper and taxon 536018. It is not a whole-genome species test or proof of a particular enzyme pathway.
Context_only
Source:
ncbi_australicum
TaxID 536018 resolves the species name used in the publication and sequence submission. It does not identify WSM2073 as the assay strain or establish a species-wide mineral-forming phenotype.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Bixbyite-(Mn) and bixbyite-(Fe) rows, PDF page 27; introductory definitions of redefined status and special procedures.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14) -
cnmnc21h: Miyawaki, Hatert, Pasero and Mills (2022). IMA Commission on New Minerals, Nomenclature and Classification, Newsletter 64. European Journal of Mineralogy 34:1-6, section 3.2 on page 6: IMA 21-H redefinition of bixbyite and definition of its Mn/Fe members.
https://doi.org/10.5194/ejm-34-1-2022 (accessed 2026-10-14) -
bohu2015: Bohu et al. (2015). Characterization of pH dependent Mn(II) oxidation strategies and formation of a bixbyite-like phase by Mesorhizobium australicum T-G1. Frontiers in Microbiology 6:734. Complete 15-page publisher PDF, full XML, Figures 1-7 and supplementary Table S1.
https://doi.org/10.3389/fmicb.2015.00734 (accessed 2026-10-14) -
ncbi_australicum: NCBI Taxonomy 536018. Mesorhizobium australicum, current species node.
https://api.ncbi.nlm.nih.gov/datasets/v2/taxonomy/taxon/536018/dataset_report (accessed 2026-10-14) -
ena_tg1: ENA/INSDC HG932494.1. Mesorhizobium australicum partial 16S rRNA gene, strain T-G1; 1354 bp, original isolate provenance, taxon 536018 and Bohu2015 publication cross-reference.
https://www.ebi.ac.uk/ena/browser/view/HG932494.1 (accessed 2026-10-14)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-14T06:29:59Z |
codex (GPT-6; Codex) | CREATE | Add the redefined Mn-dominant mineral identity and qualified T-G1 culture formation evidence, retaining phase, control and assay limits. |
Record source: data/records/bixbyite-mn.yaml