Cummingtonite-(<i>P</i>2<sub>1</sub>/<i>m</i>): Crystal-structure refinement, Mössbauer spectroscopy and infrared spectroscopy, and some aspects of classification of the magnesium-iron-manganese amphiboles
Bibliographic record
Abstract
Abstract The crystal structure of cummingtonite-(P21/m) was characterised by single-crystal structure-refinement, infrared spectroscopy and 57Fe Mössbauer spectroscopy. Previous cummingtonite-(P21/m) specimens characterised have Mn2+ as the dominant constituent at M(4) but this amphibole has Fe2+ dominant at M(4). The formula of the amphibole was corrected for minor exsolved calcium-amphibole and is (Mg5.66Fe2+1.28Mn0.06)Σ7.00Si8.00O22(OH)2. The crystal structure (a = 9.4885(19), b = 18.040(4), c = 5.2891(11) Å, β = 102.06(3)°, V = 885.4(3) Å3, space group P21/m and Z = 2), was refined to an R1-index of 3.34% for 2338 observed reflections. Site-occupancy refinement gave the following site-populations: M(1) = 1.972(8) Mg + 0.028 Fe2+, M(2) = 2.000 Mg, M(3) = 0.989(6) Mg + 0.011 Fe2+, M(4) = 0.815(8) Mg + 1.125 Fe2+ + 0.060 Mn2+ apfu. Infrared spectroscopy in the principal (OH)-stretching region shows two peaks, at 3367 and 3652 cm–1, that were assigned to the local arrangements M(1)MgM(1)MgM(3)Mg–OH and M(1)MgM(1)Fe2+M(3)Mg–OH (≈ M(1)MgM(1)MgM(3)Fe2+–OH) with relative intensities in accord with the refined site-populations. 57Fe Mössbauer spectrum shows three quadrupole-split doublets with parameters indicative of octahedrally coordinated Fe2+ at M(4) and M(1,2,3), and octahedrally coordinated Fe3+ that occurs in exsolved calcium amphibole. All three techniques indicate a small amount of Fe2+ at M(1,2,3) despite the fact that there is more than sufficient CMg to completely fill the M(1,2,3) sites: 5.66 Mg pfu. Issues involving the current and possible future nomenclature and classification of the magnesium-iron-manganese amphiboles are discussed in detail.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| 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) | 0.002 | 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".