Uranophane mineral
Uranophane is the calcium uranyl silicate hydrate mineral Ca(UO2)2(SiO3OH)2(H2O)4·H2O in the September 2026 IMA list. It is the historical alpha polymorph; the former beta polymorph is the distinct species parauranophane. CNMNC approved these names in August 2022. The IMA entry Rn, 2022 s.p. records a renaming by special procedure, not a unique approval accession. Natural Nopal I material was distinguished from the beta polymorph by powder diffraction in the 1993 study. Separate experiments on natural Shinkolobwe crystals and synthetic uranophane powders support abiotic laboratory dissolution and surface alteration. Neither the uranium constituent nor mineral occurrence establishes a criticality designation, microbial mechanism or industrial recovery.
Microbial & Biochemical Mechanisms (2)
Abiotic acid dissolution and surface alteration of uranophane
other
Acid exposure produced etch pits and compositionally altered surfaces on natural crystals, and released uranium from separately prepared synthetic powders. Silica-rich material and inferred uranyl-bearing secondary phases complicate interpreting dissolved uranium as a dissolution rate. Molecular explanations involving cation coordination and dissolution followed by reprecipitation remain interpretations.
Experimental Context & Analytical Limits:
Schindler and colleagues used natural crystals from Shinkolobwe, Democratic Republic of Congo, at room temperature, one mounted crystal per surface experiment in 5 mL solution. HCl batch treatments at initial pH 2 lasted 10 or 30 minutes; distinct flow experiments replaced fluid every 30 seconds. Most surface observations followed washing and drying, with delays of 12 hours to three days. The separate powder arm used XRD-checked synthetic uranophane, 50 mg in 25 mL, with shaking and sampling after 10, 30 and 45 minutes. Initial-pH-2 solutions contained HCl alone or 0.5 mol/L MgCl2, SrCl2, CaCl2, BaCl2 or Pb(NO3)2. ICP-OES measured solution chemistry; untreated surfaces and the HCl-only arm provided comparisons. Independent reactor replication was not clearly specified. No isolated uranium product was assayed.
Schindler and colleagues used natural crystals from Shinkolobwe, Democratic Republic of Congo, at room temperature, one mounted crystal per surface experiment in 5 mL solution. HCl batch treatments at initial pH 2 lasted 10 or 30 minutes; distinct flow experiments replaced fluid every 30 seconds. Most surface observations followed washing and drying, with delays of 12 hours to three days. The separate powder arm used XRD-checked synthetic uranophane, 50 mg in 25 mL, with shaking and sampling after 10, 30 and 45 minutes. Initial-pH-2 solutions contained HCl alone or 0.5 mol/L MgCl2, SrCl2, CaCl2, BaCl2 or Pb(NO3)2. ICP-OES measured solution chemistry; untreated surfaces and the HCl-only arm provided comparisons. Independent reactor replication was not clearly specified. No isolated uranium product was assayed.
Curated Evidence Points:
Support
Source:
schindler2009
Sections 3.1-3.3 and 4.3-4.12, Figures 4-10 and Tables 1-4 support acid-driven dissolution and altered surfaces. Figure 10 and page 2525 rank the early increase in solution uranium as Pb(NO3)2-HCl below BaCl2-HCl, CaCl2-HCl, HCl, SrCl2-HCl and MgCl2-HCl, respectively. This is a synthetic-powder comparison, not a parauranophane result or an industrial extraction yield. The mineral-only HCl treatment also dissolved uranophane, without microbial involvement.
Partial
Source:
schindler2009
Page 2525 explicitly rejects calculating exact dissolution rates from uranium release because secondary phases also control solution U. Calcium could not be measured in the CaCl2 and BaCl2 matrices; page 2530 further warns that the Ca arm's greater saturation prevents a direct inference about its cation's promoting or inhibiting effect. Table 1 gives final powder-solution pH values 2.1-2.5 after 45 minutes, and 5.4 after three hours from initial pH 3.5. These are not fixed-pH assays. XRD did not identify a uranyl-hydroxy-hydrate in recovered powder solids; proposed specific surface products, including billietite, were not independently established mineral identifications. Section 5.9 leaves leaching versus dissolution-reprecipitation unresolved.
Partial
Source:
schindler2009
The original has unresolved labels: Figure 3d says 30 minutes for alpha-uranophane at pH 3.5 whereas Table 3 and section 4.6 say three hours; Table 3 labels the fibrous beta Ca treatment 60 minutes whereas Table 4 lists Ca treatment at 30 minutes. Figure 8e names PbCl2 while Table 1 and section 4.9 specify Pb(NO3)2. Figure 10d's caption says 20-30 minutes where the methods and page 2525 use 10-30 minutes. No fitted spectrum, disputed arm duration, graph-derived absolute rate or unique surface-phase assignment is imported as a measurement.
Abiotic hydrothermal crystallization of uranophane
other
Aqueous uranyl acetate, calcium acetate and sodium metasilicate produced the alpha polymorph in laboratory hydrothermal preparations. Successful uranophane synthesis did not establish synthesis of parauranophane or an equilibrium boundary between the two minerals.
Experimental Context & Analytical Limits:
Cesbron and colleagues report about fifty preparations across several uranyl-silicate products, principally in Teflon-lined steel autoclaves at 150 degrees C, with some trials as low as 60 degrees C. NH4OH or HCl adjusted pH, which was measured on opening the autoclave rather than continuously at reaction temperature. Experiment-specific durations, complete reagent amounts, yields and replicate counts were not supplied.
Cesbron and colleagues report about fifty preparations across several uranyl-silicate products, principally in Teflon-lined steel autoclaves at 150 degrees C, with some trials as low as 60 degrees C. NH4OH or HCl adjusted pH, which was measured on opening the autoclave rather than continuously at reaction temperature. Experiment-specific durations, complete reagent amounts, yields and replicate counts were not supplied.
Curated Evidence Points:
Support
Source:
cesbron1993
Pages 304-305 report uranophane at Ca:U:Si = 2:1:1 and measured pH 3.5-9.5, with better diffraction crystallinity below pH 5. At pH 5, preparations spanned U:Si = 1:1 to 1:6; increasing silica reduced crystallinity. The source provides no recovered-mass yield.
Partial
Source:
cesbron1993
Pages 304 and 308 state that beta-uranophane was not obtained under the tested conditions, despite its occurrence at Nopal I. This is a bounded negative result, not proof of thermodynamic impossibility. Natural diffraction samples and synthetic preparations are distinct arms. The unknown controls on polymorph formation and stability prevent extrapolation to long-term radionuclide retention in a repository or industrial recovery.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Uranophane row, PDF page 224; formula, Rn and 2022 s.p.; definitions on page 1. Fresh authority PDF and original row visually inspected.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-16) -
cnmnc2022: Miyawaki R, Hatert F, Pasero M, Mills SJ (2022). IMA Commission on New Minerals, Nomenclature and Classification (CNMNC), Newsletter 69. European Journal of Mineralogy 34:463-468. DOI 10.5194/ejm-34-463-2022. Section 3, page 467: approved August 2022 renaming of uranophane-alpha to uranophane and uranophane-beta to parauranophane.
https://ejm.copernicus.org/articles/34/463/2022/ (accessed 2026-10-16) -
cesbron1993: Cesbron F, Ildefonse P, Sichere MC (1993). New mineralogical data on uranophane and beta-uranophane; synthesis of uranophane. Mineralogical Magazine 57:301-308. DOI 10.1180/minmag.1993.057.387.12. Complete original eight-page article, Figures 1-4 and Tables 1-2 inspected through RRUFF; natural polymorph identification on pages 303-307 and synthesis on pages 304-305 and 308. The 2018 publisher posting is not the study year.
https://doi.org/10.1180/minmag.1993.057.387.12 (accessed 2026-10-16) -
schindler2009: Schindler M, Freund M, Hawthorne FC, Burns PC, Maurice PA (2009). Dissolution of uranophane: An AFM, XPS, SEM and ICP study. Geochimica et Cosmochimica Acta 73:2510-2533. DOI 10.1016/j.gca.2009.01.031. Complete coauthor-hosted original, all 24 pages, Tables 1-4 and Figures 1-13 inspected. Methods pages 2512-2518, powder results pages 2524-2525, and interpretive limitations pages 2526-2531.
https://doi.org/10.1016/j.gca.2009.01.031 (accessed 2026-10-16)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-16T00:37:22.892351Z |
codex (GPT-6; codex) | CREATE | Added current-name uranophane with distinct natural-crystal dissolution and synthetic-powder release evidence, qualified hydrothermal synthesis and preserved source contradictions. |
Record source: data/records/uranophane.yaml