CMMMech
CMMMech > Mineral > Schoepite

Schoepite mineral

Schoepite is a uranyl oxide hydroxide hydrate mineral with the current IMA formula (UO2)4O(OH)6·6H2O, distinct from metaschoepite, elemental uranium and products historically called dehydrated schoepite. The September 2026 IMA list gives approved status A and 1962 s.p.; this special-procedure year is not a conventional approval accession or the 1923 original-description year. Plášil's 2018 study of natural Shinkolobwe crystals supports orthorhombic Pbca, revising the earlier P21ca model. For museum specimen RGM2708, Table 2 gives a = 16.7810(5), b = 14.7044(4), c = 14.2985(5) angstrom, Z = 8 at 297 K. The linked CIF agrees on these cell parameters but prints formula_sum H36 O21 U4 and calculated density 4.9865 g/cm3, conflicting with the paper's formula, which implies H18 O21 U4, and density 4.918 g/cm3. The CIF metadata are not used to redefine the species. The second crystal's Table 1 residual 0.0343 also differs from the prose's two-to-three-percent wording. No criticality, microbial activity or industrial uranium recovery is inferred.

Microbial & Biochemical Mechanisms (1)

Abiotic alteration of natural schoepite to metaschoepite-bearing material

other

Natural schoepite crystals altered during laboratory manipulation, storage and X-ray examination. Diffraction supports formation of metaschoepite, sometimes in mixtures with residual schoepite and dehydrated schoepite. Partial loss of interlayer water and associated structural rearrangement are proposed explanations, not directly measured reaction stoichiometry or a universal humidity threshold.

Experimental Context & Analytical Limits:
Finch et al. studied Shinkolobwe museum specimens B3616 and 91.62. B3616 crystals came from its surface, whereas 91.62 crystals were extracted from its interior. Coating and exposure histories differed. The observation below is the same experiment already represented from the product perspective in cmmmech:metaschoepite, not an independent replication. The 2018 structural specimens are separate.
Curated Evidence Points:
Page 837 and Table 3 describe B3616 crystal sc-c(1) changing overnight at 20 degrees C during a ten-hour X-ray exposure to sc-c(2), identified as metaschoepite. Its a dimension decreased approximately two percent from 14.26 to 14.0 angstrom in that paper's axis setting; b and c did not change detectably. The initially shortened a dimension suggested pre-existing minor metaschoepite. This is not an initially pure conversion yield, controlled dehydration rate or isolated-product recovery.
Pages 836-839 preserve contrasting stability and mixed products: coated B3616 crystals and uncoated 91.62 crystals remained stable during more than two years of study, although the latter later altered. Altered B3616 cores and rims differed in phase content. Poor diffraction limited complete structural solution, and the authors did not test reversibility. Their proposed loss of one-sixth of interlayer water was not a direct water-loss assay. Separate heating in water and at 120 degrees C in air produced different or uncertain mixtures and is not pooled with sc-c(1).
Context_only Source: plasil2018
Pages 67-69 and S1 reconsider the earlier acentric schoepite model in favor of Pbca. Seven weak pre-averaging reflections violated the b-glide in the newer data; the successful refinement and strong parameter correlations in the acentric model underlie the author's conclusion. The modern axis setting and revised structural model must not be silently substituted into the 1998 experiment's cell labels. Calculated structural complexity is not a measured dehydration barrier, rate or recovery efficiency.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Schoepite row, PDF page 194; status and special-procedure definitions page 1. Fresh official PDF and row inspected. The row cites American Mineralogist 8 (1923), 67 and Journal of Geosciences 63 (2018), 65.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-16)
  2. plasil2018: Plášil J (2018). The crystal structure of uranyl-oxide mineral schoepite, [(UO2)4O(OH)6](H2O)6, revisited. Journal of Geosciences 63:65-73. DOI 10.3190/jgeosci.252. Complete nine-page published original inspected, including Tables 1-7 and Figures 1-3. Natural specimen RGM2708 and sample 2; current symmetry and comparison with the 1996 model pages 65-68. Thermodynamic discussion pages 69-71 is interpretation, not a new transformation experiment.
    https://doi.org/10.3190/jgeosci.252 (accessed 2026-10-16)
  3. plasil2018_si: Plášil (2018), linked supplementary S1 PLATON ADDSYM report and schoepite CIF, both inspected. S1 supports Pbca reassignment of the earlier coordinates. CIF cell and refinement fields agree with the main RGM2708 table, but formula and density metadata conflict as retained above; placeholder journal/title fields also remain. Reflection data are present; refinement was not rerun.
    https://www.jgeosci.org/detail/jgeosci.252/supplementary/ (accessed 2026-10-16)
  4. finch1998: Finch RJ, Hawthorne FC, Ewing RC (1998). Structural relations among schoepite, metaschoepite and dehydrated schoepite. Canadian Mineralogist 36:831-845. Complete 15-page published PDF inspected during round110; experimental text, Table 3 and Figures 3-5 rechecked for this record. Pages 835-839 distinguish natural specimens and alteration arms; pages 839-843 discuss proposed structural mechanisms. No DOI verified in the bounded search.
    https://www.rruff.net/doclib/cm/vol36/CM36_831.pdf (accessed 2026-10-16)

Curation History

Timestamp Curator Action Summary
2026-10-16T04:28:04.165520Z codex (GPT-6; codex) CREATE Added current schoepite identity and natural alteration evidence, preserving revised symmetry, source conflicts and shared-experiment limits.

Record source: data/records/schoepite.yaml