Insights into the crystal chemistry of the serandite–schizolite–pectolite series
Bibliographic record
Abstract
ABSTRACT The compositional series {Na} [[M1+M2](Ca2XMn2–2X)Si3O8(OH)] includes the minerals serandite (X = 0), schizolite (X = 0.5), and pectolite (X = 1). Six crystals are structurally and chemically characterized in detail (four from Ilímaussaq, Greenland; two from Mont Saint-Hilaire, Québec, Canada): one serandite, one pectolite, and four schizolite crystals. Those originating from Greenland show up to 0.05 apfu LREE3+ (La + Ce + Pr + Nd + Eu + Gd). For each, all H atoms were located, and final R1 factors were below 4.4% ( = 2.35%). The results are compared with previously published crystal structure data from an additional 16 samples, originating from worldwide (mostly) igneous environments. Across the series, for all investigated samples, Ca and Mn order preferentially at the octahedral M1 and M2 sites, respectively, following the exchange M2Ca + M1Mn ↔ M1Ca + M2Mn. Site-occupancies closely adhere to a two-site distribution coefficient, calculated here to be K = 20.0(5), for ideal mixing where activity coefficients approach unity. For the above order-disorder exchange, ΔHex is calculated to be –1.77 kcal. With knowledge of K, site assignment and species determination may be accurately made solely with compositional data, where 0 ≤ ΣCa < 0.55 apfu, serandite; 0.55 ≤ ΣCa < 1.45 apfu, schizolite; and 1.45 ≤ ΣCa ≤ 2 apfu, pectolite, with the dominant-constituent rule mandating M1Ca < M1Mn (M2Ca < M2Mn), serandite; M1Ca > M1Mn (M2Ca < M2Mn), schizolite; and M1Ca > M1Mn (M2Ca > M2Mn), pectolite. Polyhedral distortion and structural strain at the M1 and M2 sites, calculated using the equations of Robinson et al. (1971) and solutions to Kirchhoff network equations, respectively, show a predictable, cooperative variation across the entire compositional series; however, prominent discontinuities in distortion and strain behavior are observed for the schizolite composition.
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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".