Soddyite mineral
Soddyite is the uranyl silicate hydrate mineral (UO2)2(SiO4)(H2O)2, with orthorhombic Fddd symmetry and U:Si = 2:1. The September 2026 IMA list records grandfathered status G and original-description year 1922; that year is not an IMA approval accession. Plášil's 2018 study provides new single-crystal diffraction data for natural museum material. The separate Giammar and Hering experiments used synthetic powder and demonstrate abiotic dissolution, silicon-dependent uranium release and precipitation of an incompletely resolved secondary uranium phase. These laboratory observations do not establish a microbial mechanism, a criticality-list designation, recovered uranium product or industrial use.
Microbial & Biochemical Mechanisms (1)
Abiotic dissolution with secondary uranium precipitation
other
Synthetic soddyite released uranium and silicon into solution. In batch experiments dissolved uranium subsequently decreased while silicon continued increasing, supporting dissolution coupled to precipitation of a clarkeite-like sodium uranyl oxide hydrate. The exact secondary phase and its nucleation site remained unresolved. Flow experiments with 100 micromol/L added dissolved silicon showed lower net uranium release than the no-added-silicon arm; this is not an isolated product recovery measurement or proof of a unique molecular inhibition pathway.
Experimental Context & Analytical Limits:
All dissolution experiments were at 22 +/- 2 degrees C, in 0.01 mol/L NaNO3 and 5 mmol/L MES adjusted with NaOH to pH 6.00. Two separately synthesized, XRD-checked powders were used in batch tests at 0.13 and 0.12 g/L; suspensions were equilibrated with atmospheric CO2 and capped during reaction. Later batch pH stability was estimated from buffer capacity rather than monitored. Two stirred flow reactors of about 50 mL held 0.41-0.42 g/L solid, with measured hydraulic residence times of 1.14-1.26 hours without added Si and 1.22-1.88 hours with 100 micromol/L added Si; effluent pH was 6.00-6.06. Filtered solution U and Si were measured by ICP-MS. Flow rates of U release were calculated from effluent concentrations, residence time, solid loading and a measured BET area of 3.15 square metres/g, averaging after ten reactor volumes. The paper does not clearly specify independent replication of each flow arm. Solids were examined by XRD, Raman spectroscopy and SEM.
All dissolution experiments were at 22 +/- 2 degrees C, in 0.01 mol/L NaNO3 and 5 mmol/L MES adjusted with NaOH to pH 6.00. Two separately synthesized, XRD-checked powders were used in batch tests at 0.13 and 0.12 g/L; suspensions were equilibrated with atmospheric CO2 and capped during reaction. Later batch pH stability was estimated from buffer capacity rather than monitored. Two stirred flow reactors of about 50 mL held 0.41-0.42 g/L solid, with measured hydraulic residence times of 1.14-1.26 hours without added Si and 1.22-1.88 hours with 100 micromol/L added Si; effluent pH was 6.00-6.06. Filtered solution U and Si were measured by ICP-MS. Flow rates of U release were calculated from effluent concentrations, residence time, solid loading and a measured BET area of 3.15 square metres/g, averaging after ten reactor volumes. The paper does not clearly specify independent replication of each flow arm. Solids were examined by XRD, Raman spectroscopy and SEM.
Curated Evidence Points:
Support
Source:
giammar2002
Sections 2-3 and Figures 3-8 support uranium release and later precipitation in batch suspensions. The reported linear-fit batch release rates are 0.064 micromol U per square metre per hour over 4-198 hours and 0.035 micromol Si per square metre per hour over 90-700 hours; the fitting windows differ. New needle-like solids appeared by SEM at 1683 hours. The secondary-phase interpretation combines a new XRD peak near 15 degrees 2-theta, Raman differences and morphology; residual soddyite remained in the solids.
Partial
Source:
giammar2002
Section 3.3 gives calculated flow uranium-release rates of 0.70 +/- 0.11 and 0.45 +/- 0.06 micromol per square metre per hour for zero and 100 micromol/L added Si, respectively. Section 4.4 and the abstract instead give 0.71 and 0.44; the source does not explain that small numerical difference or define the reported +/- statistic. These alternatives are preserved rather than combined. Effluent concentrations changed during each run, and remaining reactor U decreased by 11.7% and 7.4%. The added-Si arm was calculated to be nearer saturation, so the comparison does not independently isolate a surface-inhibition mechanism. Slower batch dissolution was proposed to reflect transport limitation, not demonstrated as such.
Partial
Source:
giammar2002
Section 3.2 states that powder XRD cannot distinguish clarkeite from structurally related sodium uranates; Raman comparison used a separately synthesized clarkeite-like reference. No unique secondary mineral or hydration stoichiometry is asserted here. Silicon samples after 700 hours were lost during an unsuccessful ICP-MS run, and adherence of solids to flask walls affected total-suspension U. Figure 5 labels the final XRD sample 1680 hours while the text and SEM use 1683 hours. Section 3.2 gives late dissolved U as 1.9-2.5 micromol/L, whereas section 4.1 uses 1.9-2.7. Table 2 and Figure 9 recalculate or model equilibria; they are not new measured phase fractions or independent solubility determinations.
Context_only
Source:
plasil2018
Section 2.1, Table 2 and soddyite_final.cif support the distinct natural mineral identity, using Museum of Natural History in Luxembourg material, with R1 = 1.92% for 499 reflections above I > 3 sigma(I). This is not the powder used in the 2002 dissolution experiment. Table 2 gives c = 18.6576(11) angstrom whereas the CIF gives 18.6576(7); the uncertainty difference is unresolved. The crystallographic study provides no dissolution or microbial test.
Sources & References
-
ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Soddyite row on PDF page 202 and status/year definitions on page 1. Fresh original authority PDF visually checked; formula (UO2)2(SiO4)(H2O)2, G, 1922.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-16) -
plasil2018: Plášil J (2018). Mineralogy, Crystallography and Structural Complexity of Natural Uranyl Silicates. Minerals 8(12):551. DOI 10.3390/min8120551. Complete 15-page original, publisher XML and supplementary crystallographic archive inspected. Despite the Review article label, section 2.1 and Table 2 report new natural-crystal data; soddyite identity is also discussed in section 3.3. Supplement inspected: soddyite_final.cif. Museum collection provenance is distinct from the illustrated Musunoi and Swambo specimens in Figure 7.
https://doi.org/10.3390/min8120551 (accessed 2026-10-16) -
giammar2002: Giammar DE, Hering JG (2002). Equilibrium and kinetic aspects of soddyite dissolution and secondary phase precipitation in aqueous suspension. Geochimica et Cosmochimica Acta 66(18):3235-3245. DOI 10.1016/S0016-7037(02)00927-4. Complete original 11-page article from the public GeologyScience repository visually inspected, including Tables 1-2 and Figures 1-9; Crossref and publisher metadata agree.
https://doi.org/10.1016/S0016-7037(02)00927-4 (accessed 2026-10-16)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-16T01:34:23.343810Z |
codex (GPT-6; codex) | CREATE | Added soddyite with natural identity and synthetic abiotic dissolution, preserving uncertain secondary phases and conflicting rate summaries. |
Record source: data/records/soddyite.yaml