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Metaschoepite mineral

Metaschoepite is a uranyl oxide hydroxide hydrate mineral, distinct from schoepite, elemental uranium and the products historically called dehydrated schoepite. The September 2026 IMA list gives (UO2)8O2(OH)12·10H2O and grandfathered status G; 1960 is the original description year, not an approval accession. Historical schoepite II terminology is retained only as context. Natural crystals undergoing alteration and synthetic metaschoepite exposed to controlled humidity are separate evidence populations. The synthetic formula [(UO2)4O(OH)6]·5H2O is the same ideal stoichiometry on a four-uranium basis. No criticality, microbial activity or industrial recovery is inferred from these laboratory mineral transformations.

Microbial & Biochemical Mechanisms (2)

Abiotic formation during alteration of natural schoepite

other

Natural schoepite crystals transformed to metaschoepite during laboratory storage and examination. Diffraction identified the mineral relationship; loss of interlayer water, hydrogen-bond rearrangement and strain effects were proposed explanations.

Experimental Context & Analytical Limits:
Finch et al. examined Shinkolobwe museum specimens B3616 and 91.62. Crystals from the surface of B3616 differed from crystals obtained from the interior of 91.62. Manipulation, coating and exposure history mattered. This was not a controlled humidity rate experiment or a microbial incubation.
Curated Evidence Points:
Pages 836-838 and Table 3 describe crystal sc-c(1) changing to sc-c(2) overnight at 20 degrees C during a ten-hour X-ray exposure. The a dimension decreased by approximately two percent, while b and c did not change detectably; diffraction supported metaschoepite. A shortened initial a dimension suggested some metaschoepite was already present before the visible transformation. This observation is not a conversion yield or a homogeneous reaction-rate measurement.
Uncoated 91.62 crystals did not visibly alter during the more-than- two-year study, but the authors report later alteration of those crystals. Coated B3616 crystals and uncoated manipulated crystals behaved differently. The one-sixth interlayer-water-loss account is a structural interpretation, not a direct water-loss measurement in this arm. The authors did not establish reversibility and could not solve a complete metaschoepite structure from their poor-quality crystals. Their apparently stable natural mixtures do not establish universal stability in air.

Abiotic humidity-associated dehydration of synthetic metaschoepite

other

Synthetic metaschoepite developed an alpha-UO2(OH)2-type dehydration product during storage over silica desiccant or a moderately humid salt solution. Diffraction and spectroscopy support hydrate and dehydrated-phase mixtures. The exact local structure of the product remains model-dependent; it is not assigned here as a pure natural mineral species or an isolated uranium recovery product.

Experimental Context & Analytical Limits:
Kirkegaard et al. prepared two batches through uranyl nitrate heating at 300 degrees C for 24 hours, hydration of the resulting amorphous UO3 with D2O at 80 degrees C, and ambient evaporation and rinsing. Powder samples in ceramic crucibles were stored in separate bell jars near 22 degrees C and stirred weekly. Tables 1-2 describe A from batch 1 over saturated NaCl in D2O at approximately 78 percent relative humidity for 41 days; B from batch 2 over K2CO3 in D2O at approximately 45 percent for 18 days; C from batch 1 over silica desiccant for 41 days, with its relative humidity unspecified. Salt-based humidities use calculations at 20 degrees C and are approximate for the experiment. D2O preparation does not establish retained complete deuteration after ambient handling.
Curated Evidence Points:
Figures 3-4 and Table 2 give neutron-diffraction Rietveld-fitted weight percentages of metaschoepite and the alpha-UO2(OH)2-type phase, respectively: A 95.5(2) and 4.5(3), B 70.7(1) and 29.3(1), C 10.8(5) and 89.2(6). Parenthetical uncertainties are retained as printed. These are fitted phase fractions, not gravimetric water losses, isolated-product yields or reaction rates. C remained a mixture despite the discussion's essentially-complete wording. No conversion of A to schoepite was observed under this particular humid-storage condition; universal irreversibility was not tested.
Page S2 and Figure S2 show a minor dehydration-product peak in the second batch before storage, attributed to synthesis material above the waterline. Initial scans also differed in duration, twelve versus one hour. B therefore cannot be treated as an initially pure replicate of A or C. Figure S8 shows that neutron patterns alone do not distinguish the competing local structural models. Figure S4 labels A as 75 percent relative humidity, while the main Tables 1-2 specify 78 percent; this discrepancy is retained.
Discussion page 19 calls B's duration sixteen days, conflicting with eighteen in Tables 1-2. The authors explicitly cannot confirm a faster desiccation rate because equilibration times differ. Separate batches, an initial minor dehydrated component and possible handling effects also limit comparisons. Their synthetic dry-storage result narrows earlier apparent air-stability claims without equating uncontrolled natural-specimen histories to these controlled laboratory arms. No threshold humidity, field rate or independently replicated recovery efficiency is inferred.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Metaschoepite row, PDF page 142; status and year definitions page 1. Fresh official PDF and mineral row inspected. The row cites American Mineralogist 45 (1960), 1026 and Inorganic Chemistry 58 (2019), 7310.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-16)
  2. finch1998: Finch RJ, Hawthorne FC, Ewing RC (1998). Structural relations among schoepite, metaschoepite and dehydrated schoepite. Canadian Mineralogist 36:831-845. Complete 15-page published PDF inspected, including Tables 1-4 and Figures 1-8. Natural samples and experiments pages 835-839; transformation interpretation pages 839-843. No DOI verified in the bounded bibliographic search.
    https://www.rruff.net/doclib/cm/vol36/CM36_831.pdf (accessed 2026-10-16)
  3. kirkegaard2019: Kirkegaard MC, Niedziela JL, Miskowiec A, Shields AE, Anderson BB (2019). Elucidation of the Structure and Vibrational Spectroscopy of Synthetic Metaschoepite and Its Dehydration Product. Inorganic Chemistry 58:7310-7323. DOI 10.1021/acs.inorgchem.9b00460; PMID 31099558. Complete 43-page accepted manuscript from OSTI 1720254 inspected; locators below use manuscript pagination, not final publisher pagination. Methods and Table 1 pages 4-8; Figures 3-4 and Table 2 pages 10-11; stability discussion pages 17-19. The final published layout was not independently inspected.
    https://doi.org/10.1021/acs.inorgchem.9b00460 (accessed 2026-10-16)
  4. kirkegaard2019_si: Kirkegaard et al. (2019), supporting information for DOI 10.1021/acs.inorgchem.9b00460, ACS Figshare article 8144057, file 15177548. Complete nine-page supplement inspected. Additional synthesis details and Figure S2 page S2; Figure S4 page S4; alternative structural-model comparison Figure S8 page S7.
    https://acs.figshare.com/articles/journal_contribution/8144057 (accessed 2026-10-16)

Curation History

Timestamp Curator Action Summary
2026-10-16T03:51:36.379421Z codex (GPT-6; codex) CREATE Added current mineral identity and distinct natural and synthetic transformation evidence with source discrepancies and phase-mixture limits.

Record source: data/records/metaschoepite.yaml