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Rhabdophane-(La) mineral

Rhabdophane-(La) is the lanthanum-dominant hydrated phosphate mineral listed by IMA-CNMNC with ideal formula La(PO4)·H2O and renamed status Rn, 1987 s.p., in September 2026. This entry does not provide a numbered IMA approval identifier. It is distinct from elemental lanthanum, mixed rare-earth phosphate material, rhabdophane-(Ce) and anhydrous monazite-(La). Ondrejka et al. (2018) characterized natural La-dominant members within mixed, compositionally zoned rhabdophane-group grains from the Velence Hills, Hungary, using electron microprobe and Raman spectroscopy. Their analyses include substitutions and mixed end-member contributions; neither every grain nor every La-Nd-rich zone is pure rhabdophane-(La). Natural-grain hydration is not measured by oxide totals alone. The 2019 erratum requires inclusion of Fe in formula calculations without recognizing an Fe end-member. Shelyug et al. (2018) separately characterized synthetic La rhabdophane and its thermal conversion to monazite. Their fitted monoclinic model and total-water coefficient 0.804 describe that preparation, not a universal species assay or revised IMA formula. No microbial mechanism, isolated lanthanum recovery, industrial deployment or inherited criticality designation is curated.

Microbial & Biochemical Mechanisms (1)

Abiotic thermal conversion of synthetic La rhabdophane

other

A synthetic La rhabdophane powder was thermally converted to La monazite by heating 200 mg in air at 1100 degrees C for 6 hours. Powder X-ray diffraction identified the starting hydrated phase and the monazite product. This is a laboratory mineral transformation, not a microbial extraction experiment or a measured isolated-lanthanum recovery yield.

Experimental Context & Analytical Limits:
The synthesis series used analytical lanthanide chlorides; for La, the precursor was LaCl3·7H2O. Four mmol of lanthanide chloride was mixed with 5 M H3PO4 at a metal:P molar ratio of 1:1.03, stirred for 15 minutes at 60 degrees C and held in Teflon for two weeks at 90 degrees C. Powders were washed twice with deionized water, then ethanol, centrifuged and air-dried overnight. The resulting rhabdophane and heated monazite powders were stored airtight at room temperature for approximately a year before calorimetry. PXRD/Rietveld analysis fitted the hydrated powder using a monoclinic C2 model and the heated product as P21/n monazite; reported single-phase status is limited by diffraction detection. Separate 15-20 mg TGA/DSC runs in air used 10 degrees C/min over 30-1000 degrees C, with blank correction. La total-water content was reported as 0.804 H2O per LaPO4, including adsorbed and structural water. This is not a site-resolved water occupancy. The series-level 700-950 degrees C transformation interval is not adopted as an exact La equilibrium threshold; the transformation was not reversed.
Curated Evidence Points:
Material Preparation and Powder X-ray Diffraction, page 2, specify the synthesis, 1100 degrees C/6-hour treatment and structural models. Figure 1 shows the La starting/product diffraction traces; Table 1 and Figure 3/Table 2 report the phase and thermal characterization. These support the bounded abiotic conversion of this synthetic powder.
The abstract's stated water-content trend with ionic radius conflicts with the values in Table 2, and prose on pages 4-5 gives conflicting directions for temperature trends; those generalized trends are not adopted. Total mass loss does not independently resolve structural versus adsorbed water. The irreversible heating test and thermodynamic calculations do not establish an equilibrium transition temperature, biological causation or industrial deployment.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. PDF page 184, Rhabdophane-(La): La(PO4)·H2O, Rn, 1987 s.p., USA. Status definitions pages 1-2; renamed status and the special-procedure year do not supply a numbered approval.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-15)
  2. ondrejka2018: Ondrejka M, Bacik P, Sobocky T, Uher P, Skoda R, Mikus T, Luptakova J and Konecny P (2018). Minerals of the rhabdophane group and the alunite supergroup in microgranite: products of low-temperature alteration in a highly acidic environment from the Velence Hills, Hungary. Mineralogical Magazine 82:1277-1300. DOI 10.1180/mgm.2018.137. Complete original; analytical limits and Raman methods pages 1280-1283, natural-grain composition pages 1284-1285, representative La-dominant columns in Table 4 page 1290, Figure 7 page 1291 and Raman comparison Figure 10 page 1295. Interpretation of Fe in formula calculations on page 1296 is corrected in 2019.
    https://doi.org/10.1180/mgm.2018.137 (accessed 2026-10-15)
  3. ondrejka2019_erratum: Ondrejka et al. (2019). Minerals of the rhabdophane group and the alunite supergroup in microgranite: products of low-temperature alteration in a highly acidic environment from the Velence Hills, Hungary - ERRATUM. Mineralogical Magazine 83:321. DOI 10.1180/mgm.2019.13. Complete publisher correction: page 1296 should say that Fe2+ and Fe3+ should be included in formula calculation; possible substitutions do not define a valid Fe end-member.
    https://doi.org/10.1180/mgm.2019.13 (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/A2; preparation and PXRD page 2, La diffraction traces Figure 1 and Table 1 page 3, thermal characterization Figure 3 and Table 2 page 4. Total water includes adsorbed and structural contributions. The same synthetic series was used in Mesbah et al. (2017); it is not an independent replication of those synthesis samples.
    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 La-dominant hydrated phosphate with natural composition context, the published Fe-formula erratum, and a bounded abiotic thermal conversion of synthetic material.

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