THE CRYSTAL CHEMISTRY OF THE SCAPOLITE-GROUP MINERALS. I. CRYSTAL STRUCTURE AND LONG-RANGE ORDER
Bibliographic record
Abstract
Scapolite-group minerals are a group of rock-forming framework aluminosilicates common in a wide variety of igneous and metamorphic rocks. They have the general formula M 4 [ T 12 O 24 ] A , where M represents Na, K, Ca, Sr, Ba and Fe 2+ , T stands for Si, Al, (Fe 3+ ), and A represents Cl, (CO 3 ), (SO 4 ). They constitute a non-binary solid-solution series involving the end members marialite (Na 4 [Al 3 Si 9 O 24 ] Cl, Ma ) and meionite (Ca 4 [Al 6 Si 6 O 24 ] CO 3 , Me ). The crystal structures of eighteen scapolite-group minerals from Me 4.9 to Me 92.8 [ Me = 100 ∑ M 2+ /∑( M 2+ + M + )] have been refined with Mo K α X-radiation. The crystals, a 12.045–12.208, c 7.564–7.586 A, V 1099.7–1130.1 A 3 , I 4/ m or P 4 2 / n , Z = 2, were analyzed with an electron microprobe subsequently to collection of the X-ray intensity data. There are subtle differences between the behavior of the distinct T tetrahedra in the I 4/ m and P 4 2 / n structures. For Si and Al, determinative curves for the assignment of site populations from T –O> distances were developed for each T site in each structure type, and T -site populations were assigned from these curves. In I 4/ m marialite, there is no Al at the T (1) site. In P 4 2 / n scapolite, Al is strongly ordered at T (2), and Si is strongly ordered at T (3), but this order is never complete. The A -site cation (Na, Ca, K) is [8]-coordinated in end-member marialite and is (on average) [8.5]-coordinated in end-member meionite. Each ( M ϕ n ) polyhedron shares two edges with adjacent ( M ϕ n ) polyhedra, forming a three-dimensional framework that interpenetrates the [ T 12 O 24 ] silicate framework. In (CO 3 )-bearing structures, the model proposed by previous workers, four (CO 3 ) groups arranged about the 4 axis ( I 4/ m ) or 4 axis ( P 4 2 / m ), is consistent across the series from marialite to meionite. Any (SO 4 ) present is disordered by rotation of 90° about the central 4-fold axis; in I 4/ m structures, each arrangement is 50% occupied, whereas in P 4 2 / n structures, the occupancies of the two arrangements are not required to be equal.
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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) | 0.001 | 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".