The role of Fe and cation order in the crystal chemistry of surinamite, (Mg,Fe <sup>2+</sup> ) <sub>3</sub> (Al,Fe <sup>3+</sup> ) <sub>3</sub> O[AlBeSi <sub>3</sub> O <sub>15</sub> ]: A crystal structure, Mössbauer spectroscopic, and optical spectroscopic study
Bibliographic record
Abstract
The crystal structure of surinamite from “Christmas Point,” Enderby Land, Antarctica, has been newly refined by single-crystal X-ray diffraction: VI (Mg 2.26 Fe 2+ 0.74 Fe 3+ 0.39 Al 2.61 )O IV (Al 1.00 Be 1.00 Si 3.00 )O 15 (simplified formula), space group P2/n, a = 9.915(2), b = 11.368(2), c = 9.617(2), b = 109.30(2)°, Z = 4, wR(F 2 ) = 0.074 for 4876 independent reflections. The refined site occupancies agree well with the chemical composition determined by electron microprobe analysis and with the Fe 3+ /Fe 2+ ratio estimated from stoichiometry. The surinamite structure is characterized by an ordered Al/Be/Si distribution on the tetrahedral sites and by charge ordering with extensive Mg 2+ -Fe 2+ and Al 3+ -Fe 3+ exchange on the octahedral sites. This cation ordering is distinct from that observed in related phases of the sapphirine series and aenigmatite groups, and the difference is linked to the unique structural topology of the tetrahedral chains in surinamite. Optical and Mössbauer spectra of surinamite have been fully interpreted in terms of an octahedral distribution of Fe 2+ and Fe 3+ cations that agrees very well with the X-ray site populations. Both the X-ray and Mössbauer data establish the absence of significant tetrahedral Fe and the non-uniform distribution of octahedral Fe. Intense and strongly polarized absorption bands caused by IVCT-processes in clusters of Fe 3+ and Fe 2+ iron in edgesharing octahedral sites produce the unusual color and pleochroism observed in surinamite.
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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 | 0.000 | 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".