Oscillatory zoned liddicoatite from Anjanabonoina, central Madagascar. I. Crystal chemistry and structure by SREF and 11B and 27Al MAS NMR spectroscopy
Bibliographic record
Abstract
The crystal structures of 23 samples extracted from a large slice oriented along (001) of a single crystal of liddicoatite from the Anjanabonoina granitic pegmatite in Madagascar (showing pronounced, visually discontinuous oscillatory zones and anomalous biaxiality) were refined to R 1 indices of 1.5–2.9% ( R 1 > = 1.78%). Cell parameters are in the range a ≈ 15.82–15.87, c ≈ 7.10–7.12 A. Spindle-stage measurement of 2 V gave values of 0.0° for a fragment from the (001) zone and 8(3) and 18.9(5)° for fragments from the pyramidal zone of the crystal. However, single-crystal X-ray intensity data show no deviation from 3 m Laue symmetry, indicating that there is no information in the diffraction data on any deviation from R 3 m symmetry. The T –O> distances are in the range 1.616–1.619 A, with a grand mean value of 1.6175(7) A. The occupancy of the T site was expressed as x Si + (1− x )B, and x was treated as variable in the refinement procedure. The effect of using different scattering factors ( i.e ., ionized versus neutral) on the refined site-occupancies was investigated in detail. The grand mean refined [4] B content of the T site varies from −0.04 apfu for ionized scattering-curves for O and Si to 0.25 apfu for neutral scattering-curves for O and Si, illustrating the effect of the use of different scattering curves on refined [4] B site-populations. Examination of T –O> distances as a function of aggregate cation radius for tourmalines containing [4] B and [4] Al shows a large amount of scatter, emphasizing the need for more accurate data. The limits of detection for 11 B and 27 Al in tourmaline by Magic-Angle-Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy were investigated by simulation. For minimum ( apfu ) and maximum (0.12 apfu ) contents of (paramagnetic) transition metals, the limits of detection of [4] B are~0.02 and 0.08 apfu , and of [4] Al are~0.01 and 0.01 apfu , respectively. 11 B and 27 Al MAS NMR spectroscopy gave no evidence of the presence of tetrahedrally coordinated B or Al at the T site above these detection limits in any sample. This result is in accord with our refinement results using an ionized scattering-curve for O and a neutral scattering-curve for Si, suggesting that use of these curves is giving more accurate results than refinement with neutral scattering factors. The Z –O> distances are in the range 1.904–1.907 A, with a grand mean value of 1.9047(8) A, and structure refinement indicates site-scattering values in accord with complete occupancy of the Z site by Al. Hence throughout this complexly zoned crystal, Si = 6.00 apfu and Z Al = 6.00 apfu .
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 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".