Al–Mg disorder in a gem-quality pargasite from Baffi n
Bibliographic record
Abstract
The crystal structure of gem-quality pargasite from Soper River, near Kimmirut, Baffin Island, Nunavut, Canada, (K0.24Na0.73)0.97 (Ca1.86Na0.14)2.00 (Mg4.15Fe0.07Mn0.01Al0.71Ti0.06)5.00 (Si6.45Al1.55) O22 [(OH)1.25F0.63O2–0.12]2.00, a 9.8814(6), b 17.967(1), c 5.2927(4) Å, 105.263(5)°, V 906.5 Å3, C2/m, Z = 2, has been refined to an R index of 2.9 % using 1506 observed intensities measured with MoK X-radiation. The crystal used for collection of the X-ray intensity data was then analyzed with an electron microprobe. The amphibole composition is very close to that of end-member pargasite. There is significant disorder of Al over the M(2) [1.40 Mg + 0.54 Al + 0.06 Fe3+] and M(3) [0.81 Mg + 0.17 Al + 0.02 Fe2+] sites. Such disorder has been observed in Mg-rich pargasite from a high-pressure paragenesis in the western Alps. The infrared spectrum of this amphibole in the principal OH-stretching region shows a complex envelope that can be resolved into six bands by analogy with the spectra of synthetic (OH,F)-bearing pargasite in the literature. The relative intensities of the component bands are in accord with the observed OH:F ratio in this pargasite, and indicate complete short-range disorder of OH and F. The occurrence of Al–Mg disorder over M(2) and M(3) in the Soper River pargasite, from a lower-pressure environment, indicates that this disorder is a compositional feature of pargasite, rather than a result of crystallization or equilibration at high pressure and temperature. The pattern of electron density in the A cavity of the structure may be interpreted in terms of K and Na at the A(m) site and Na at the A(2) site. Moreover, the specific site-populations are conformable with the composition of this amphibole and the most favorable patterns of short-
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".