STRUCTURE AND TOPOLOGY OF DUMORTIERITE AND DUMORTIERITE-LIKE MATERIALS
Bibliographic record
Abstract
Dumortierite, ca . (Al,□)Al 6 (BO 3 )Si 3 O 13 (O,OH) 2 , has a complex and unusual crystal structure that is shared by several minerals and an increasing number of synthetic materials, which we group together as dumortierite-like materials (DLMs). Dumortierite has a strongly pseudo-hexagonal orthorhombic structure based on rod-like double-chains of Al octahedra in a framework based on the {6·4·3·4} semi-regular planar tiling. The large hexagonal channels contain chains of face-sharing Al octahedra attached to the framework by rings of SiO 4 tetrahedra. Smaller triangular channels contain planar BO 3 groups, while in other materials the triangular channels are occupied by tetrahedral or pyramidal groups. Holtite and magnesiodumortierite are isostructural with dumortierite, while ellenbergerite, phosphoellenbergerite, ekatite, and the synthetic materials have very similar structures to dumortierite, but with hexagonal symmetry. These minerals and materials differ from one another in the identity of the metal cations occupying the framework and face-sharing chains, and in the tetrahedral, pyramidal, or triangular groups within the hexagonal and triangular channels. We write the following structure-generating function, which describes both topological and stoichiometric properties of DLMs: X ( M 2 Φ ) 3 ( T h Θ h 3 θ h ) 3 ( T t Θ t 3 θ t ) where X is the face-sharing hexagonal channel octahedrally coordinated site, M is the framework octahedrally coordinated site, T h and T t are three- to four-coordinate cation sites in the hexagonal and triangular channels, Φ is a four-coordinate anion site, Θ h and Θ t are three-coordinate basal anion sites, and θ h and θ t are one- to three-coordinate apical anion sites. We discuss various structural and crystal chemical properties of DLMs, illustrating their commonalities as variations on the theme described by the structure-generating function. We also discuss three closely related structures which involve modifications of different geometrical or topological aspects of the DLM structure: the structure of lyonsite and its synthetic analogues, the structure of satterlyite and holtedahlite, and the structure of the AB polytype of the cancrinite group of feldspathoids.
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".