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Richetite mineral

Grandfathered hydrated lead-iron-magnesium uranyl oxide hydroxide mineral with current September 2026 IMA-CNMNC approved formula (Fe3+,Mg)xPb2+8.6(UO2)36O36(OH)24(H2O)41, status G, and original-description year 1947 (not a numbered IMA approval CURIE). Originally described by Vaes (1947) from the Shinkolobwe mine, Katanga (Haut-Katanga), Democratic Republic of the Congo, richetite was structurally solved for the first time by Burns (1998) on a Shinkolobwe crystal provided by William Pinch. Electron-microprobe WDS analysis (5 points, Table 2, p. 188) detected UO3 (77.02-77.83 wt%, mean 77.43 wt%) and PbO (16.76-17.37 wt%, mean 17.06 wt%), corresponding to a U:Pb atomic ratio of 1:0.282 (10.15 Pb2+ per 36 U), whereas Fe and Mg were below the microprobe detection limit on that thin flake (~0.25 wt% FeO/MgO inferred from structure). Single-crystal SMART CCD X-ray diffraction refined in triclinic space group P1 (a = 20.9391(3), b = 12.1000(2), c = 16.3450(3) A, alpha = 103.87(1), beta = 115.37(1), gamma = 90.27(1) degrees, V = 3605.2 A3, Z = 1, R = 8.9%, S = 1.79 for 12,383 unique observed reflections with |Fo| > 4sigma_F; attempts to refine in P-1 failed) established alpha-U3O8-type uranyl oxide hydroxy-hydrate sheets [(UO2)18O18(OH)12] stacked with 13 partially occupied interlayer Pb2+ sites (8.74 Pb pfu), two octahedral M(1)/M(2) sites (modeled with 0.47(5) Fe2+ + 0.53(5) Mg2+ at M(1) and 0.30(5) Mg2+ at M(2), x = 1.30), and 41 H2O sites, yielding the 1998 structural formula MxPb8.74[(UO2)18O18(OH)12]2(H2O)41. Hydrogen positions were not directly refined, and only U and Pb atoms were modeled anisotropically. The subsequent 2017 refinement cited in the IMA Master List (American Mineralogist 102 (2017), 1771, specifying (Fe3+,Mg)x and Pb2+8.6) is behind a paywall and was not independently acquired at curation. Distinct from masuyite, fourmarierite, vandendriesscheite, curite, and elemental uranium or lead; no criticality designation, microbial mechanism, or extraction yield is asserted.

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Sources & References

  1. ima_2026_09: IMA-CNMNC, The New IMA List of Minerals, September 2026, PDF page 185, Richetite row: formula (Fe3+,Mg)xPb2+8.6(UO2)36O36(OH)24(H2O)41, status G, year 1947, country Democratic Republic of the Congo, first reference Annales de la Société Géologique de Belgique 70 (1947), B212, second reference American Mineralogist 102 (2017), 1771; column definitions on PDF page 1.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-18)
  2. burns_1998_richetite: Burns PC (1998), The structure of richetite, a rare lead uranyl oxide hydrate, Canadian Mineralogist 36:187-199. Complete 13-page primary PDF visually inspected: Shinkolobwe specimen (W. Pinch collection), SMART CCD triclinic P1 X-ray diffraction Table 1, and WDS electron-microprobe analysis Table 2 pp. 187-189; atomic coordinates, bond lengths, and bond- valence sums in Tables 3-5 pp. 190-196; interlayer Pb/Fe/Mg site-occupancy disorder and alpha-U3O8-type uranyl-sheet topology in Figures 1-2 pp. 196-198.
    https://www.rruff.net/doclib/cm/vol36/CM36_187.pdf (accessed 2026-10-18)

Curation History

Timestamp Curator Action Summary
2026-10-19T05:22:00Z antigravity CREATE Created richetite mineral record from the September 2026 IMA master list and complete 1998 Shinkolobwe triclinic P1 crystal-structure and microprobe study, preserving interlayer site-disorder and unrefined hydrogen limitations.

Record source: data/records/richetite.yaml