Cl-RICH FLUORAPATITE, DEVOID OF OH, FROM THE THREE PEAKS AREA, UTAH: THE FIRST REPORTED STRUCTURE OF NATURAL Cl-RICH FLUORAPATITE
Bibliographic record
Abstract
Abstract Apatite is the most abundant phosphate mineral on Earth and forms the foundation of the global phosphorus cycle. Interest in apatite crosses many disciplines, including geology, agriculture, material science, dentistry, and medicine, and the phase is also used extensively in many manufacturing processes. Apatite is the main source of phosphate for fertilizer, and adequate sources of apatite are essential for production of fertilizers that are necessary for feeding the world’s population. Despite the importance of the phase, the atomic arrangement of apatite is not well understood. The natural apatite anion solid solution among F, OH, and Cl (fluorapatite, hydroxylapatite, and chlorapatite, respectively) is one of those rare solid solutions wherein the atomic arrangements of the binary and ternary solid solutions are not predictable from the atomic arrangements of the endmembers of the ternary system; the steric interactions in the (F, OH, Cl) apatite anion column are complex as the three anions mix. Although the first detailed account of the atomic arrangement of binary apatites along the F-Cl join was recently reported using painstakingly synthesized samples, natural Cl-rich fluorapatite, although long-sought, had not been identified; an Earth environment that has high fugacity of F and Cl, but is devoid of OH, is rare. Here we report the atomic arrangement of a natural Cl-rich fluorapatite from the Three Peaks area of Utah (USA) that is essentially devoid of OH. The structure ( R 1 = 0.0145) of the P 6 3 / m apatite is similar to that obtained from synthetic samples, and demonstrates that solid solution along the F–Cl join in natural apatites is achieved by creation of a second F site (F b ) in the Cl-rich fluorapatite [0, 0, z ] anion column, an off-mirror site at z = 0.178, coupled with the presence of a site for Cl (Cl b ), that differs from the Cl site in endmember chlorapatite. The combination of a Cl site that relaxes toward its associated mirror plane and a neighboring F site that relaxes away from its associated mirror plane allows sufficient separation of F and Cl in the anion column for the two anions to coexist. The structure described herein is the first reported structure of a natural Cl-rich fluorapatite.
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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 | 0.001 | 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 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".