The crystal chemistry of the gedrite-group amphiboles. II. Stereochemistry and chemical relations
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Bibliographic record
Abstract
Abstract The general formula of the amphiboles of this series may be written as Na x Mg 2 (Mg (5- y ) Al y ,)(Si (8- z ) Al z )O 22 (OH) 2 , where Mg = Mg + Fe 2+ + Mn 2+ and Al = Al + Fe 3+ + Ti. The individual < T –O> distances are linear functions of their [4] Al content, and the [4] Al content is strongly ordered in the following way: T 1 B > T 1A » T 2B » T 2A. The < M 1-O>, < M 2-O> and < M 3–O> distances are linear functions of the mean ionic radius of their constituent cations. End-member compositions may be written as follows: A ☐Mg 2 Mg 5 Si 8 O 22 (OH) 2 O 22 (OH) 2 ; A ☐Mg 2 (Mg 3 Al 2 )(Si 6 Al 2 )O 22 (OH) 2 ; A NaMg 2 Mg 5 (Si 7 Al) These compositions define a plane in xyz space across which the data of Schindler et al. (2008), measured on amphiboles from amphibolites, follow a tightly constrained trajectory. Anthophyllite–gedrite amphiboles equilibrated under significantly different P-T conditions (e.g. igneous rocks, contact-metamorphic rocks) follow trends that diverge from this trajectory, with greater Na and [4] Al contents and relatively smaller [6] Al contents. Detailed examination of the local bond topology involving the A and M 2 sites indicates that the maximum degree of bond-valence compensation will occur for incorporation of A Na and M 2 Al in the ratio 4:10, and hence 2.5 A Na = M 2 Al in these amphiboles. This relation closely fits the data of Schindler et al. (2008), suggesting that the variation in chemical composition in anthophyllite–gedrite amphiboles is strongly constrained by the anion bond-valence requirements of the Pnma amphibole structure. We further suggest that different compositional trends for ortho-amphiboles equilibrated under different P-T conditions are the result of the valence-sum rule operating with (different) bond-lengths characteristic of these P-T conditions.
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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 | 0.001 |
| 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 it