Lead apatites: structural variations among Pb<sub>5</sub>(<i>B</i>O<sub>4</sub>)<sub>3</sub>Cl with <i>B</i> = P (pyromorphite), As (mimetite) and V (vanadinite)
Bibliographic record
Abstract
The crystal structure of four Pb apatite samples, Pb5(BO4)3Cl, was refined with synchrotron high-resolution powder X-ray diffraction data, Rietveld refinements, space group P63/m and Z = 2. For this isotypic series, B = P5+ is pyromorphite, B = As5+ is mimetite and B = V5+ is vanadinite. The ionic radius for As5+ (0.355 Å) is similar to that of V5+ (0.335 Å), and this is twice as large as that for P5+ (0.170 Å). However, the c unit-cell parameter for mimetite is surprisingly different from that of vanadinite, although their unit-cell volumes, V, are almost equal to each other. No explanation was available for this peculiar c-axis value for mimetite. Structural parameters such as average 〈B—O〉 [4], 〈Pb1—O9〉 [9] and 〈Pb2—O6Cl2〉 [8] distances increase linearly with V (the coordination numbers for the cations are given in square brackets). Mimetite has a short Pb2—O1 distance, so the O1 oxygen atom interacts with the 6s 2 lone-pair electrons of the Pb2+ cation that causes the Cl—Cl distance (= c/2) to increase to the largest value in the series because of repulsion, which causes the c-axis to increase anomalously. Although Pb apatite minerals occur naturally in ore deposits, they are also formed as scaly deposits in lead water pipes that give rise to lead in tap water, as was found recently in Flint, Michigan, USA. It is important to identify Pb-containing phases in water-pipe deposits.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 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".