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Rhabdophane-(Ce) mineral

Rhabdophane-(Ce) is the cerium-dominant hydrated phosphate mineral listed by IMA-CNMNC with ideal formula Ce(PO4)·H2O and renamed status Rn, 1966 s.p., in September 2026. That nomenclature entry is not a numbered approval identifier. It is distinct from elemental cerium, an unspecified mixed rare-earth phosphate and anhydrous monazite-(Ce). Synthetic Ce-rich rhabdophane prepared by replacement of Durango fluorapatite was identified by powder diffraction and thermal characterization in Bamforth et al. (2024). The fitted monoclinic structural model is study-specific; the Sm reference structure used in refinement is not a Ce-specimen accession. Ideal hydration is not an assay of every synthetic powder: Shelyug et al. (2018) reported CePO4·0.732H2O from thermogravimetry including adsorbed and structural water. Porous monazite and rhabdophane can have overlapping low electron-microprobe totals, so elemental composition or totals alone do not distinguish these phases. The curated transformation is an abiotic laboratory result. No microbial mechanism, isolated cerium recovery, industrial deployment or inherited criticality is asserted.

Microbial & Biochemical Mechanisms (1)

Abiotic acid-mediated replacement by monazite-(Ce)

other

Synthetic Ce-rich rhabdophane was replaced by monazite-(Ce) during closed-reactor experiments at 180 degrees C for 8 hours. At nominal pH approximately 1, relative crystalline phase analysis reported 98.6% replacement in 1 M phosphoric acid, compared with 6.4% in 0.1 M hydrochloric acid. These are fitted phase proportions, not isolated-product or elemental recovery yields. Diffraction and preserved aggregate textures with changed nanoscale prisms support dissolution and precipitation; the proposed rate-limiting step and fluid-boundary mechanism remain interpretations of the experiment.

Experimental Context & Analytical Limits:
Laboratory, no organisms. Starting material was produced by reacting 50 +/- 0.5 mg of 250-355 micrometre Durango fluorapatite with 15 mL of 0.1 M HCl and 0.02 M CeCl3·7H2O at 30 degrees C for 96 hours, then rinsing with water and acetone. Eleven such preparative runs supplied characterization samples and nine pooled/homogenized portions for distinct hydrothermal conditions; they are not eleven replicates of each comparison. Table 1 lists 20.9-21.1 mg portions in 15 mL fluids in 25 mL PTFE-lined reactors, while the methods prose says 20 +/- 0.1 mg; that discrepancy is unresolved. Acid composition and nominal pH are experimental comparators, not matched microbial controls. At nominal pH 3, section 3.1 calls replacement below 5%, but Figure 3 labels 4.4%, 4.7% and 6.4%; no single corrected value or kinetic law is inferred. The authors note an approximately 1% PXRD detection limit. Preparative completion is diffraction-defined, not a claim of absolute chemical purity or directly measured hydration.
Curated Evidence Points:
Sections 2.1-2.2, Table 1 and Figures 2-3 establish the stated material, comparison and relative phase conversion. Figures 6-7 show aggregate preservation and changed individual prisms; section 4.1.2 interprets coupled dissolution-precipitation. The 98.6% versus 6.4% comparison is restricted to the two nominal-pH-1 fluids and 180 degrees C/8-hour treatment.
Figure 9 is a proposed mechanism, not direct molecular tracking. The loading discrepancy between section 2.1.2 and Table 1 and pH-3 conflict between section 3.1 and Figure 3 remain unresolved. Section 4.3.2/Figure 10 demonstrates overlapping microprobe totals in independently identified phases; composition alone cannot establish that an unrelated biological Ce phosphate is rhabdophane. No microbial causality or deployment is tested.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. PDF page 184, Rhabdophane-(Ce): Ce(PO4)·H2O, Rn, 1966 s.p., United Kingdom. Status definitions pages 1-2; renamed status and special-procedure year do not supply an IMA approval number.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-15)
  2. bamforth2024: Bamforth TG, Xia F, Putnis A, Brugger J, Hu SY, Roberts MP, Suvorova A and Pring A (2024). Hydrothermal mineral replacement in the apatite-rhabdophane-monazite system: Experiments, reaction mechanisms and geological implications. Chemical Geology 666:122307. DOI 10.1016/j.chemgeo.2024.122307. Complete original; methods sections 2.1-2.7 pages 3-5, Table 1 page 4, diffraction Figure 2 page 3, replacement Figure 3 page 5, thermal Figure 4 page 6, microscopy Figures 5-7 pages 7-9 and proposed pathway Figure 9 page 11. Section 4.3.2 and Figure 10 pages 12-13 explain why low microprobe totals are not phase-specific.
    https://doi.org/10.1016/j.chemgeo.2024.122307 (accessed 2026-10-15)
  3. bamforth2024_supplement: Bamforth et al. (2024), Supplementary Material - EPMA Analysis and Data, article PII S0009254124003875, mmc1.xlsx. Two worksheets: EPMA (Analysis), standards and detection limits; EPMA (Data), sample-specific elemental weight percentages and analytical totals. Worksheet values are not recovery yields or direct water/valence measurements. This is part of the same experiment as bamforth2024, not independent replication.
    https://ars.els-cdn.com/content/image/1-s2.0-S0009254124003875-mmc1.xlsx (accessed 2026-10-15)
  4. shelyug2018: Shelyug A, Mesbah A, Szenknect S, Clavier N, Dacheux N and Navrotsky A (2018). Thermodynamics and Stability of Rhabdophanes, Hydrated Rare Earth Phosphates REPO4·nH2O. Frontiers in Chemistry 6:604. DOI 10.3389/fchem.2018.00604. Complete original and supplementary Tables A1a-c and A2; preparation and diffraction methods page 2, Figure 1 and Table 1 page 3, thermal Figure 3 and Table 2 page 4. The Ce total-water coefficient 0.732 is a powder-specific thermogravimetric estimate, not a revised IMA formula. Materials are the same synthesis series used in Mesbah et al. (2017), not an independent replication of it.
    https://doi.org/10.3389/fchem.2018.00604 (accessed 2026-10-15)

Curation History

Timestamp Curator Action Summary
2026-10-15T21:18:41Z codex (GPT-6; codex) CREATE Added the distinct Ce-dominant hydrated phosphate with a qualified abiotic hydrothermal transformation, preserving fitted phase denominators, source protocol conflicts and hydration uncertainty.

Record source: data/records/rhabdophane-ce.yaml