THE DISTRIBUTION OF CHROMIUM IN CHROMIAN PUMPELLYITE FROM SARANI, URALS, RUSSIA: A TOF NEUTRON AND X-RAY RIETVELD STUDY
Bibliographic record
Abstract
The crystal structure of chromian pumpellyite from Sarani in the Russian Urals was refined using complementary time-of-flight neutron and X-ray Rietveld methods, to investigate the crystal-chemical behavior of chromium in pumpellyite. The average chemical composition of the sample is CaO 22.06 ± 0.39, MgO 3.95 ± 0.37, Cr 2 O 3 14.39 ± 1.19, Al 2 O 3 16.71 ± 0.79, total Fe 2 O 3 0.15 ± 0.08, and SiO 2 35.73 ± 0.63 wt.% ( n = 38). The occupancy of Mg at the octahedral X site refined with the neutron-diffraction data is 0.48(3), the same as that obtained by chemical analysis. The occupancies of Cr and Al refined with the X-ray-diffraction data were 0.32(1)Cr and 0. 20Al at the X site, and 0.31Cr and 0.69Al at the Y site. Bond-valence considerations support the validity of the refined occupancies and the assumption that Cr is trivalent. Accordingly, the formula is established as Ca 8.00 (Mg 1.92 Cr 1.28 Al 0.80 ) ∑4.00 (Al 5.52 Cr 2. 48 ) ∑8.00 Si 12.00 O 42.12 (OH) 13.88 . Although Cr 3+ ions occur at both the X and Y sites, the distribution coefficient [(Cr/Al) X /(Cr/Al) Y = 3.56] indicates a stronger preference of Cr for the X site than the Y site. The unit-cell parameters were refined as a 8.8193(5), b 5.9396(3), c 19.161(1) A, β 97.603(2)° and V 994.86(9) A 3 (neutron data), and a 8.8132(2), b 5.9342(1), c 19.1466(3) A, β 97.603(2)° and V 992.54(3) A 3 (X-ray data). Substitution of chromium for aluminum at the Y site increases the mean Y –O distance by expansion of the octahedra, which causes increase in the a , b , and c dimensions. However, the mean X –O distance is not correlated with mean ionic radius at the X site. Distortion parameters of the Y site tend to decrease with increasing mean Y –O distance and volume of the site. Expansion of octahedra by ionic substitutions of larger cations for Al at the Y site thus causes a gradual change of the octahedra to a highly symmetrical and regular form.
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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 | 0.000 | 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".