Al-Si Order and Chemical Composition Model across Scapolite Solid Solutions with Evidence from Rietveld Structure Refinements
Bibliographic record
Abstract
Scapolite forms solid solutions between the end members marialite, Na4[Al3Si9O24]Cl = Me0, and meionite, Ca4[Al6Si6O24]CO3 = Me100. Al-Si order and chemical composition models are proposed for the scapolite solid solutions. These models predict the chemical composition, Al-Si order, and average <T–O> distances between Me0–Me100. These models are based on the observed order of clusters and on two solid solutions that meet at Me75 coupled with predicted chemical compositions and <T–O> distances. The [Na4·Cl]3+ and [NaCa3·CO3]5+ clusters are ordered between Me0–Me75, whereas the clusters [NaCa3·CO3]5+ and [Ca4·CO3]6+ are disordered from Me75–Me100. To confirm the structural model, the crystal structure of 27 scapolite samples between Me6–Me93 has been obtained using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinements. The structure was refined in space group P42/n for all the samples. The <T–O> distances indicate that the T1 (=Si), T2 (=Al), and T3 (=Si) sites are completely ordered at Me37.5, where the 1:1 ratio of [Na4·Cl]3+:[NaCa3·CO3]5+ clusters are ordered and gives rise to antiphase domain boundaries (APBs) based on Cl-CO3 order instead of Al-Si order. The presence of APBs based on Cl-CO3 order and cluster order indicate that neither space group P42/n nor I4/m are correct for the structure of scapolite, but the lower symmetry space group P42/n is a good approximation for modeling the average structure of scapolite. The complete Al-Si order at Me37.5 changes in a regular and predictable manner toward the end members: Me0, Me75, and Me100. The observed unit cell and several structural parameters show a discontinuity at Me75, where the series is divided into two. There is no structural evidence to support any phase transition in the scapolite series. The T1 site contains only Si from Me0–Me37.5; from Me37.5–Me100, Al atoms enter the T1 site and the <T1–O> distance increases linearly to Me100.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 teacher head, 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".