CMMMech
CMMMech > Mineral > Coffinite

Coffinite mineral

Coffinite is the uranium-bearing silicate mineral listed by IMA-CNMNC in September 2026 as U(SiO4)·nH2O, with grandfathered status G and original-description year 1956. That year is not a numbered mineral approval. Coffinite is distinct from uraninite, dissolved uranium, uranium-bearing ores and synthetic mixtures that merely contain uranium and silicon. The variable water term is not a measured hydration number for every specimen. Suzuki et al. (2016) identified natural coffinite nanoparticles in the L3 calcium-carbonate layer of a fracture-filling vein from borehole 07MI07 at the Mizunami Underground Laboratory, Japan. Elemental mapping, selected-area electron diffraction and lattice imaging support their assignment; the particles occur with aluminosilicate and contain other elements including phosphorus, zirconium and yttrium. The authors' proposed microbial origin is an interpretation of a natural setting, not a controlled organism-specific formation experiment. The separate laboratory mechanism below concerns newly formed coffinite on a prepared UO2 pellet, not bioleaching of that natural vein or testing of irradiated spent fuel. No criticality designation is inherited from elemental uranium, and no isolated-metal yield or industrial operation is asserted.

Microbial & Biochemical Mechanisms (1)

Abiotic coffinite formation at a prepared UO2 pellet surface

other

Contact of a prepared UO2 pellet with silicate-bearing, initially uranium-spiked solution produced a coffinite-bearing surface layer. Grazing-incidence diffraction and particle-scale microscopy support formation of coffinite alongside residual UO2. Dissolution of an oxidized surface layer followed by precipitation is the authors' proposed pathway; the uranium contribution from the pellet versus the added dissolved stock was not separately traced. This is an abiotic laboratory formation observation, not a demonstrated microbial mechanism, complete pellet conversion, or product yield.

Experimental Context & Analytical Limits:
The single reported leaching experiment used a synthesized, sintered and polished UO2 pellet of 1.105 ± 0.001 g in 100 mL of solution at 25 degrees C in an argon glove box with reported oxygen at or below 1 ppm. Initial total silicon was (1.77 ± 0.03) x 10^-3 mol/L; dissolved uranium was added to reach about 10^-5 mol/L and the solution was adjusted to pH 9. The solution was slightly undersaturated with respect to amorphous silica according to the methods, although the abstract calls it saturated. The reported values after 100 days were pH 8.76 ± 0.03 and Eh -55 ± 35 mV. The pellet was repeatedly removed for surface characterization. Solution samples were centrifuged and analyzed by ICP-AES or ICP-MS; a 3 kDa ultrafiltration step was added after 328 days. Three analytical replicates and twice their standard deviation describe concentration measurements, not three independent leaching reactors. No parallel unspiked, no-pellet or silicate-free time-course comparator is reported. The initially characterized pellet provides a before-exposure comparison. No organisms or microbial inoculum were used.
Curated Evidence Points:
Figure 4a shows additional grazing-incidence diffraction peaks assigned to tetragonal coffinite after 155 days, clearer after 210 days, while UO2 peaks remain. Figure 6 combines Si-bearing particle chemistry, lattice spacings of 0.469 and 0.281 nm, a Fourier transform and electron diffraction with a neighboring UO2 comparison. This is stronger phase evidence than particle shape or aqueous uranium depletion alone. Figures 1 and S2 characterize the starting pellet; Figure 1 XPS resolves an oxidized surface contribution despite the predominantly U(IV) bulk. Figures 5 and S3 show surface alteration and grain detachment, but do not measure coffinite purity or total yield.
Figure 2 records declining aqueous uranium in a solution that already contained added uranium, so it does not quantify uranium extracted from the pellet or recovered as coffinite. The changed late sampling filtration further limits pooling all points as one dissolved fraction. No isotope or mass-balance experiment establishes the relative sources of uranium in the precipitate. Figure 3 and Table 1 are thermodynamic calculations with selected constants and crystalline UO2 explicitly excluded from that diagram; they do not directly measure aqueous uranium oxidation states. The main text places terminal TEM characterization after 371 days, whereas Figure 6 says 339 days; that timing is unresolved here. The Results cite Figure S1 for the pellet, but the original SI labels S1 as powder and S2 as pellet. Methods describe gentle drying for removal and analysis yet state that the ESEM preparation never dried the specimen; the exact hydration history across observations is therefore not established. These limits leave the observed phase formation supported without proving the proposed pathway, a fixed hydrate stoichiometry or repository-scale performance.
Context_only Source: suzuki2016
Figures 2-3 locate U-bearing nanoparticles in natural fracture carbonate and combine elemental signals, diffraction and lattice images consistent with coffinite. This is an independent natural occurrence, not a replication of the prepared-pellet experiment. The proposed enzymatic reduction and carbonate precipitation by heterotrophic microorganisms were not tested with cultures, killed-cell or abiotic controls. Nearby sulfide-bearing particles appear in Supplementary Figure 1; their presence and the study's spatial observations do not resolve all abiotic alternatives. U-Pb ages are model-derived and incorporate an estimated matrix effect without a coffinite-matched standard. Geological retention inferred from those ages does not demonstrate an engineered remediation lifetime or industrial deployment.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Definitions on PDF page 1; Coffinite row on page 48, U(SiO4)·nH2O, G, 1956. Retained original re-inspected; issuing website still links this edition on the access date.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-12)
  2. suzuki2016: Suzuki Y, Mukai H, Ishimura T, Yokoyama TD, Sakata S, Hirata T, Iwatsuki T and Mizuno T (2016). Formation and Geological Sequestration of Uranium Nanoparticles in Deep Granitic Aquifer. Scientific Reports 6, 22701. DOI 10.1038/srep22701. Complete original six-page article, Figures 1-3, and original supplementary DOCX: Tables 1-4, Figures 1-2 and Notes 1-2. Natural phase identification is on pages 2-3 and Figure 3; microbial interpretation and dating limitations on page 4 and Supplementary Note 2.
    https://doi.org/10.1038/srep22701 (accessed 2026-10-12)
  3. szenknect2020: Szenknect S et al. (2020). Coffinite formation from UO2+x. Scientific Reports 10, 12168. DOI 10.1038/s41598-020-69161-1. Complete original ten-page article, Figures 1-6, Table 1, and original supplementary DOCX Figures S1-S3. Experimental results pages 2-6; leaching and characterization methods pages 5-8. Original embedded supplement graphics were inspected separately where the local DOCX rendering clipped or omitted image content.
    https://doi.org/10.1038/s41598-020-69161-1 (accessed 2026-10-12)

Curation History

Timestamp Curator Action Summary
2026-10-12T12:35:48.998735Z codex (GPT-6; codex) create Added coffinite identity, qualified natural occurrence and an abiotic laboratory formation observation from complete original articles and supplements. Preserved synthetic/natural boundaries, source conflicts, uranium-stock and control limits; deferred unavailable microbial leaching methods rather than inventing an organism mechanism.

Record source: data/records/coffinite.yaml