INVESTIGATIONS OF CRYSTAL-CHEMICAL VARIABILITY IN LEAD URANYL OXIDE HYDRATES. II. FOURMARIERITE
Bibliographic record
Abstract
Structures have been refined for twelve crystals of fourmarierite from various localities in the Democratic Republic of Congo, and one synthetic crystal. Single-crystal diffraction data were collected using MoKa X-radiation and a CCD-based detector mounted on a Bruker three-circle diffractometer. All crystals have orthorhombic symmetry, space group Bb21m. The natural crystals have similar unit-cell parameters: a 14.00–14.03, b 16.40–16.48, c 14.32–14.38 Å. The parameters for the synthetic crystal, which contains less Pb than the natural crystals, are a 13.938(2), b 16.638(3), c 14.672(2) Å. The structures refined to agreement indices (R1) in the range of 3.6 to 6.2%. The structure of fourmarierite contains uranyl pentagonal bipyramids that share edges and corners to form sheets oriented parallel to (001). There are two distinct Pb2+ cations and eight H2O groups located in the interlayer. On the basis of the structure refinements, the site occupancy of Pb(1) in the natural crystals is typically deficient, ranging from 71 to 100%, whereas the site occupancy of Pb(2) is ~100 % in the crystals studied. In the synthetic crystal the Pb(1) and Pb(2) occupancies are 13 % and 87%, respectively. Increase of the Pb content is correlated with a minor increase in the a unit-cell parameter, as well as large decreases in the b and c unit-cell parameters, and the unit-cell volume. The substitution O2 – $ (OH) – at two anion sites [O(12) and O(15)] in the sheet of uranyl polyhedra provides the charge-balance mechanism associated with interlayer cation variation. The structural formula for fourmarierite may be written as Pb1–x[(UO2)4O3–2x(OH)4+2x](H2O)4, Z = 8, with the constituents of the sheet of uranyl polyhedra enclosed in square braces.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".