Penikisite, BaMg<sub>2</sub>Al<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>(OH)<sub>3</sub>, isostructural with bjarebyite
Bibliographic record
Abstract
The bjarebyite group of minerals, characterized by the general formula BaX(2)Y(2)(PO(4))(3)(OH)(3), with X = Mg, Fe(2+) or Mn(2+), and Y = Al or Fe(3+), includes five members: bjarebyite BaMn(2+) (2)Al(2)(PO(4))(3)(OH)(3), johntomaite BaFe(2+) (2)Fe(3+) (2)(PO(4))(3)(OH)(3), kulanite BaFe(2+) (2)Al(2)(PO(4))(3)(OH)(3), penikisite BaMg(2)Al(2)(PO(4))(3)(OH)(3), and perloffite BaMn(2+) (2)Fe(3+) (2)(PO(4))(3)(OH)(3). Thus far, the crystal structures of all minerals in the group, but penikisite, have been determined. The present study reports the first structure determination of penikisite (barium dimagnesium dialuminium triphosphate trihydroxide) using single-crystal X-ray diffraction data of a crystal from the type locality, Mayo Mining District, Yukon Territory, Canada. Penikisite is isotypic with other members of the bjarebyite group with space group P2(1)/m, rather than triclinic (P1 or P-1), as previously suggested. Its structure consists of edge-shared [AlO(3)(OH)(3)] octa-hedral dimers linking via corners to form chains along [010]. These chains are decorated with PO(4) tetra-hedra (one of which has site symmetry m) and connected along [100] via edge-shared [MgO(5)(OH)] octa-hedral dimers and eleven-coordinated Ba(2+) ions (site symmetry m), forming a complex three-dimensional network. O-H⋯O hydrogen bonding provides additional linkage between chains. Microprobe analysis of the crystal used for data collection indicated that Mn substitutes for Mg at the 1.5% (apfu) level.
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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 | 0.000 |
| 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) | 0.002 | 0.001 |
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".