The incorporation of fluorine in tourmaline: internal crystallographic controls or external environmental influences?
Bibliographic record
Abstract
The manner in which F is incorporated into the tourmaline structure depends on internal influences such as crystallographic constraints and on external influences such as temperature, pressure, local mineral assemblage and fluid composition. Tourmaline has a general formula XY3Z6(T 6O18)(BO3)3V3W, with the most common site-occupancies being: X = Ca2+, Na1+, K 1+, X□ (vacancy); Y= Li1+, Mg2+, Fe2+, Mn2+, Al3+, Cr3+, Fe 3+; Z = Al3+, Mg2+, Fe3+, Cr 3+; T= Si4+, Al3+; B = B3+; V= [0(3)] = OH1-, O2-; W= [O(I)] = OH1-, F 1-, O2-. Of particular importance for understanding F 1- incorporation in tourmaline is that F1- occurs solely at the O(1) site. Substitution of F1- at this site is influenced by the occupancy (total charge) of the X and the Y sites. The X site is generally occupied by cations of variable charge (+1 or +2) or is vacant (zero charge). There are three K-site cations, which can have charges of +1, +2, +3 or +4. However, the charge of the local bond-valence arrangements of the K-site cations are most commonly between +6 (e.g., Mg3) and +7 (e.g., Mg 2Al). Because of local bonding of the O(1)-site anion to three neighboring K-site cations and an X-site cation, the charges at the X and K sites affect the F1- occupancy at the W site. Disorder of Mg and Al at the K and Z sites influences the local charge, and consequently, the F content. The accumulated data on tourmaline verify the general crystallographic influences. A summary of >8800 tourmaline compositions from different lithologic environments illustrates that for tourmaline with an average X-site charge exceeding +0.9, there is a range from O to a maximum of 1.0 apfu F. As the X-site charge decreases, the maximal amount of F decreases, with the maximal amount of F being less than 0.2 apfu for those tourmalines with an X-site charge of less than +0.5. Petrological factors superimpose local environmental influences on F concentrations. The presence of minerals with a fixed high F content, such as fluorite, local assemblages of minerals and the degree of fractionation in a magma or fluid control the amount of F that is available to tourmaline within the crystallographic constraints imposed by local X- and K-site charge.
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How this classification was reachedexpand
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 | 0.000 | 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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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 teacher head, 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".