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Weeksite mineral

Potassium uranyl silicate hydrate mineral with current September 2026 IMA-CNMNC approved formula (K)2(UO2)2(Si5O13)(H2O)2·2H2O, status A, and special-procedure approval year 1962 s.p. (not a numbered IMA-XXXX-YYY accession). Outerbridge, Staatz, Meyrowitz, and Pommer (1960) described the holotype from opal-fluorite-calcite veinlets in porphyritic rhyolite at the Autunite No. 8 claim, east side of the Thomas Range, Juab County, Utah, USA, and documented nine additional occurrences in Utah, California, New Mexico, Wyoming, Pennsylvania, Texas, Arizona, and Chihuahua, Mexico. Microchemical analysis of ~100 mg of purified Thomas Range type material (Table 3, p. 46: SiO2 33.6, UO3 51.5, K2O 5.5, BaO 1.4, CaO 1.1, Na2O 0.7, Al2O3 0.6, CO2 0.3, H2O 6.6, Fe2O3 <0.1, sum 101.3 wt%) and single-crystal precession / powder X-ray diffraction led the 1960 authors to propose the orthorhombic Pnnb formula K2(UO2)2(Si2O5)3·4H2O (a = 14.26(2), b = 35.88(10), c = 14.20(2) A, Z = 16). Later structural studies cited in the IMA Master List (including the paywalled second reference Mineralogical Magazine 90 (2026), 653, which was not acquired at curation) revised the silicate-sheet stoichiometry from (Si2O5)3 (6 Si per 2 U) to (Si5O13) (5 Si per 2 U); both the 1960 analytical formula and the current IMA formula are retained with explicit attribution. Outerbridge et al. (1960) also demonstrated laboratory hydrothermal synthesis of weeksite and its Na analogue in sealed Pyrex tubes at 150 degrees C. Distinct from haiweeite, boltwoodite, uranophane, and elemental uranium; no criticality designation, microbial mechanism, or industrial recovery yield is asserted.

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Microbial & Biochemical Mechanisms (1)

Weeksite other Laboratory hydrothermal synthesis of w

Laboratory hydrothermal synthesis of weeksite and its sodium analogue in sealed Pyrex tubes

other

Heating alkaline uranyl nitrate solutions adjusted to pH 10.0 or 11.2 with KOH or NaOH inside sealed Pyrex glass tubes at 150 degrees C (~70 lbs/in2) for at least three days crystallized synthetic weeksite (with KOH) or its isostructural sodium analogue (with NaOH), using the etched Pyrex tube wall as the sole source of dissolved silica. In several runs boltwoodite co-precipitated with weeksite or its Na analogue.

Experimental Context & Analytical Limits:
Experiments by A. M. Pommer reported in Outerbridge et al. (1960), pp. 46-48 and Tables 3-4, tested 16 runs (G-33 through G-188) in sealed Pyrex tubes at 150 degrees C (calculated internal pressure ~70 psi) for at least 3 days. Solutions contained 0.025 M or 0.05 M uranyl nitrate (with 0.05 M vanadyl sulfate present only in the first four exploratory NaOH runs G-33, G-52, G-53, G-55), adjusted to pH 10.0 or 11.2 with NaOH (runs G-33 to G-166) or pH 11.2 with KOH (runs G-167 to G-188), with or without sodium/potassium carbonate buffer and wood shavings. Reaction products were identified by X-ray powder diffraction (Table 4 footnote 1 and Table 5). Only 35 mg of the synthetic Na analogue (run G-143) was chemically analyzed (Table 3, column 2); there was insufficient synthetic K-weeksite for wet-chemical analysis, and fractional uranium conversion yields were not reported.
Curated Evidence Points:
Pages 47-48 and Table 4 document that KOH runs at pH 11.2 with 0.05 M uranyl nitrate yielded X-ray-verified weeksite as the sole crystalline product in runs G-170, G-174, G-182, G-184, G-187, and G-188 (both with and without carbonate buffer and wood), whereas runs G-167 and G-179 yielded dominant boltwoodite with minor weeksite. Parallel NaOH runs (G-55, G-143, G-166) yielded the pure sodium analogue of weeksite, whose 35 mg chemical analysis (Table 3, G-143: SiO2 33.9, UO3 52.0, Na2O 7.2, H2O 8.1, C from wood 0.3, total 101.5 wt%) and powder XRD pattern (Table 5) matched natural weeksite.
Because silica was supplied by alkaline attack on the Pyrex reaction vessel rather than a metered silicate reagent, dissolved silica activity, solid-product mass yields, and chemical composition of the synthetic K-phase were not quantitatively determined.

Sources & References

  1. ima_2026_09: IMA-CNMNC, The New IMA List of Minerals, September 2026, PDF page 233, Weeksite row: formula (K)2(UO2)2(Si5O13)(H2O)2·2H2O, status A, year 1962 s.p., country USA, first reference American Mineralogist 45 (1960), 39, second reference Mineralogical Magazine 90 (2026), 653; column definitions on PDF page 1.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-18)
  2. outerbridge_1960_weeksite: Outerbridge WF, Staatz MH, Meyrowitz R, Pommer AM (1960), Weeksite, a new uranium silicate from the Thomas Range, Juab County, Utah, American Mineralogist 45:39-52. Complete 14-page primary PDF visually inspected: Autunite No. 8 holotype and nine additional localities pp. 39-43; physical and optical properties Table 1 pp. 43-44; spectrographic and microchemical analyses of natural weeksite (100 mg) and synthetic Na-analogue (35 mg) in Tables 2-3 pp. 44-47; hydrothermal synthesis at 150 degrees C in sealed Pyrex tubes in Table 4 pp. 47-48; X-ray powder and precession data Table 5 pp. 48-51.
    https://www.rruff.net/doclib/am/vol45/AM45_39.pdf (accessed 2026-10-18)

Curation History

Timestamp Curator Action Summary
2026-10-19T05:22:00Z antigravity CREATE Created weeksite mineral record from the September 2026 IMA master list and complete 1960 original description, preserving the 1960 (Si2O5)3 versus current (Si5O13) formula revision and documenting the 150 degrees C sealed-Pyrex-tube hydrothermal synthesis mechanism.

Record source: data/records/weeksite.yaml