THE DISTRIBUTION OF CHROMIUM IN CHROMIAN PUMPELLYITE FROM SARANI, URALS, RUSSIA: A TOF NEUTRON AND X-RAY RIETVELD STUDY
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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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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 | 0.002 | 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