Rhodochrosite mineral
Rhodochrosite is the manganese carbonate mineral Mn(CO3). The September 2026 IMA-CNMNC list gives status A and the entry '1962 s.p.'; this special procedure notation is not a numbered new-mineral accession. The Handbook of Mineralogy places it in the calcite group and describes hydrothermal, metamorphic, carbonatite and sedimentary occurrences. This species owner is distinct from elemental manganese, dissolved Mn(II), mixed manganese ore, kutnohorite and the synthetic colloidal Mn(IV) oxide used in the experiment below. The curated mechanism concerns laboratory formation of rhodochrosite during bacterial reduction of that oxide, not extraction from a natural rhodochrosite feed. No manganese criticality designation, isolated mineral recovery yield or industrial deployment is inherited.
Microbial & Biochemical Mechanisms (1)
Rhodochrosite formation during bacterial manganese oxide reduction
biomineralization
Microbial
Associated Organisms:
Shewanella oneidensis MR-1 (NCBITaxon:211586)
Live MR-1 reduction of synthetic colloidal Mn(IV) oxide in lactate-replete, low-phosphate medium was accompanied by formation of crystalline rhodochrosite. Time-resolved Mn X-ray absorption spectra and diffraction of collected solids support conversion through reduced Mn species followed by carbonate precipitation. Lactate oxidation supplying inorganic carbon and alkalinity is the authors' mechanistic interpretation; inorganic carbon production was not independently quantified here. The study does not establish an enzyme-specific requirement, a unique electron-transfer route, a cell-surface nucleation site or a universally biological origin for rhodochrosite.
Experimental Context & Analytical Limits:
A stirred 1 L modified M1 medium contained approximately 6.3 mM freshly synthesized colloidal MnO2, 20 mM lactate and no added phosphate for the carbonate-forming arm. The authors distinguish this poorly ordered oxide from crystalline birnessite or pyrolusite. Medium was deoxygenated with nitrogen for 45 min, adjusted to pH 8, maintained under nitrogen and circulated through the XAS flow cell at about 1 mL/s. MR-1 was grown aerobically in 1 L LB at 25-30 degrees C to OD600 about 1.2, centrifuged at 3000 rpm for 5 min, resuspended in a small amount of LB, and added as 5-10 mL cell paste after initial oxide spectra were acquired. That temperature describes precultivation; a separate reaction temperature is not specified. The final cell concentration, full modified-M1 recipe and stock authentication are not supplied; the medium is adapted from a cited cultivation reference. Inoculum-associated carryover therefore also limits a literal phosphate-free interpretation. High cell and oxide concentrations were chosen to complete beamline experiments within about 12-14 h, rather than to reproduce natural sediment conditions. Replicate experiments were performed, but no uniform replicate count or pooled uncertainty is given for every phase time course.
A stirred 1 L modified M1 medium contained approximately 6.3 mM freshly synthesized colloidal MnO2, 20 mM lactate and no added phosphate for the carbonate-forming arm. The authors distinguish this poorly ordered oxide from crystalline birnessite or pyrolusite. Medium was deoxygenated with nitrogen for 45 min, adjusted to pH 8, maintained under nitrogen and circulated through the XAS flow cell at about 1 mL/s. MR-1 was grown aerobically in 1 L LB at 25-30 degrees C to OD600 about 1.2, centrifuged at 3000 rpm for 5 min, resuspended in a small amount of LB, and added as 5-10 mL cell paste after initial oxide spectra were acquired. That temperature describes precultivation; a separate reaction temperature is not specified. The final cell concentration, full modified-M1 recipe and stock authentication are not supplied; the medium is adapted from a cited cultivation reference. Inoculum-associated carryover therefore also limits a literal phosphate-free interpretation. High cell and oxide concentrations were chosen to complete beamline experiments within about 12-14 h, rather than to reproduce natural sediment conditions. Replicate experiments were performed, but no uniform replicate count or pooled uncertainty is given for every phase time course.
Curated Evidence Points:
Support
Source:
johnson2016
Figure 2B and SI Figures S2, S4 and S5 support rhodochrosite formation in the high-lactate, low-phosphate arm. S4 compares the final solid with rhodochrosite, other carbonates and Mn oxide standards; S5 shows the development of matching peaks in sequentially collected solids. Samples were collected on 2 micrometre filters, air-dried and mostly measured by synchrotron XRD 3-4 weeks later. The authors argue against post-sampling oxidation, but do not provide an immediate wet-solid XRD comparison. In-situ XAS complements this delayed diffraction evidence. The description of rhodochrosite as the sole crystalline product does not exclude amorphous material, biomass, adsorbed Mn or dissolved Mn and is not proof of a pure recovered mineral product.
Partial
Source:
johnson2016
The final high-lactate XAS spectrum is fitted as 73% rhodochrosite standard and 27% aqueous Mn(II) in the results; Figure 2 summarizes this approximately as 75% and 25%. The combined Rh+Mnaq spectrum is subsequently an internal endmember, whose Table S2 contribution reaches 1 at t12. That value is not 100% rhodochrosite or a gravimetric recovery yield. Table S1 distinguishes the pure standard from this internally measured mixture; reference selection and linear combination fitting are model-dependent, with typical component uncertainty about 10% and stated XAS sensitivity of roughly 5-10% of total Mn. The free or dissolved Mn interpretation also has limits: the authors note that much of the Mn(II) spectral signal may be associated with residual particles.
Support
Source:
johnson2016
SI Figure S1 shows substantially unchanged Mn absorption spectra for more than 5 h with colloidal oxide and 20 mM lactate but no MR-1, supporting absence of detectable direct lactate reduction or beam reduction over that interval. This is a bounded no-cell control, not a complete-duration kinetic comparison, a killed-cell assay or a matched inorganic-carbon/pH precipitation control. No genetic or inhibitor experiment resolves direct cellular electron transfer versus soluble mediators in this study.
Partial
Source:
johnson2016
Table 1 and Figures 2A and 2C demonstrate condition dependence. With 4.3 mM added phosphate and 20 mM lactate, the principal reduced product was a Mn(II)-phosphate phase, spectrally similar but not identical to hureaulite, rather than the rhodochrosite-forming arm. With no added phosphate but only three additions of 0.5 mM lactate, residual Mn(IV) and a feitknechtite-like Mn(III) component persisted alongside Mn(II); no carbonate component was fitted in Table S2. These observations do not support unconditional rhodochrosite formation during bacterial Mn reduction or a uniquely identified obligatory Mn(III) enzymatic intermediate.
Context_only
Source:
johnson2016
Figure 3 examines distinct abiotic sulfide and ferrous-iron reduction arms in the same base medium. Excess reductant produced Mn(II)-dominated spectra without observed carbonate; these arms lacked the inorganic carbon generated in the biological interpretation. The paper explicitly recognizes that carbonate-bearing abiotic systems could instead form Mn carbonates. Its controls therefore do not establish rhodochrosite as a unique biosignature. Iron-bearing precipitates in the ferrous-iron arm, supported by SI Figures S6-S7, are separate from the biological rhodochrosite product.
Context_only
Source:
johnson2016
Table S3 reports supernatant Mn measured by ICP-MS in separate replicate reactions after centrifugation and acid dilution. Its low-phosphate replicate was substantially slower than the beamline time course and extended to 24 h; pH is supplied to aid comparison. These solution concentrations are not a simultaneous phase mass balance or mineral recovery yield, and ICP-MS alone does not distinguish free Mn(II) from other Mn species. Main Figure 2B and SI Figure S2 also differ in the year printed on one product trace, 11-26-15 versus 11-26-13; that label discrepancy is not silently used to assign independent replicate identities or exact kinetics.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Definitions on PDF page 1 and Rhodochrosite row on page 185: Mn(CO3), A, 1962 s.p. Original-description reference dated 1813. Retained issuing-authority PDF re-inspected after fresh verification that the issuing site's current list link identifies this edition.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-12) -
handbook_rhodochrosite: Handbook of Mineralogy, Rhodochrosite, Mn2+CO3. Complete original one-page datasheet, version 1, copyright 2001-2005: calcite-group identity and natural-occurrence context. Its cell and powder-pattern data are explicitly labelled synthetic.
https://handbookofmineralogy.org/pdfs/rhodochrosite.pdf (accessed 2026-10-12) -
johnson2016: Johnson JE, Savalia P, Davis R, Kocar BD, Webb SM, Nealson KH and Fischer WW (2016). Real-Time Manganese Phase Dynamics during Biological and Abiotic Manganese Oxide Reduction. Environmental Science & Technology 50(8):4248-4258. DOI 10.1021/acs.est.5b04834. Complete author-hosted typeset pre-pagination main, pages A-K: methods C-D, Table 1, Figures 1-3, results E-H. Complete 16-page original Supporting Information, Tables S1-S3 and Figures S1-S7, especially control S1 and rhodochrosite XRD S4-S5. SI checksum matches the institutional CaltechAUTHORS repository inventory.
https://doi.org/10.1021/acs.est.5b04834 (accessed 2026-10-12) -
ncbi_mr1: NCBI Taxonomy, taxon 211586, Shewanella oneidensis MR-1, strain-level entry. A name mapping for the reported MR-1 organism, not independent authentication of the experimental inoculum.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=211586&mode=info (accessed 2026-10-12)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-12T14:02:46.669472Z |
codex (GPT-6; codex) | create | Added authority-grounded rhodochrosite and qualified laboratory formation during MR-1 manganese oxide reduction, preserving phase-model, preparation, control and condition-dependent limits. |
Record source: data/records/rhodochrosite.yaml