The structures of marialite ( <i>M</i> <i>e</i> <sub>6</sub> ) and meionite ( <i>M</i> <i>e</i> <sub>93</sub> ) in space groups <i>P</i> 4 <sub>2</sub> / <i>n</i> and <i>I</i> 4/ <i>m</i> , and the absence of phase transitions in the scapolite series
Bibliographic record
Abstract
The crystal structures of marialite ( M e 6 ) from Badakhshan, Afghanistan and meionite ( M e 93 ) from Mt. Vesuvius, Italy were obtained using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinements. Their structures were refined in space groups I 4/ m and P 4 2 / n , and similar results were obtained. The M e 6 sample has a formula Ca 0.24 Na 3.37 K 0.24 [Al 3.16 Si 8.84 O 24 ]Cl 0.84 (CO 3 ) 0.15 , and its unit-cell parameters are a =12.047555(7), c =7.563210(6) Å, and V =1097.751(1) Å 3 . The average ⟨T1-O⟩ distances are 1.599(1) Å in I 4/ m and 1.600(2) Å in P 4 2 / n , indicating that the T1 site contains only Si atoms. In P 4 2 / n , the average distances of ⟨T2-O⟩=1.655(2) and ⟨T3-O⟩=1.664(2) Å are distinct and are not equal to each other. However, the mean ⟨T2,3-O⟩=1.659(2) Å in P 4 2 / n and is identical to the ⟨T2′-O⟩=1.659(1) Å in I 4/ m . The ⟨M-O⟩ [7]=2.754(1) Å (M site is coordinated to seven framework O atoms) and M-A=2.914(1) Å; these distances are identical in both space groups. The M e 93 sample has a formula of Na 0.29 Ca 3.76 [Al 5.54 Si 6.46 O 24 ]Cl 0.05 (SO 4 ) 0.02 (CO 3 ) 0.93 , and its unit-cell parameters are a =12.19882(1), c =7.576954(8) Å, and V =1127.535(2) Å 3 . A similar examination of the M e 93 sample also shows that both space groups give similar results; however, the C–O distance is more reasonable in P 4 2 / n than in I 4/ m . Refining the scapolite structure near M e 0 or M e 100 in I 4/ m forces the T2 and T3 sites (both with multiplicity 8 in P 4 2 / n ) to be equivalent and form the T2′ site (with multiplicity 16 in I 4/ m ), but ⟨T2-O⟩ is not equal to ⟨T3-O⟩ in P 4 2 / n . Using different space groups for different regions across the series implies phase transitions, which do not occur in the scapolite series.
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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 | 0.000 | 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 | 0.000 |
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".