Fibrous Tourmaline: A Sensitive Probe of Fluid Compositions and Petrologic Environments
Bibliographic record
Abstract
Tourmaline supergroup minerals with fibrous morphology record and respond to changing conditions in fluid-rich hydrothermal environments. Based on published data, hand-specimen and optical observations, and new chemical analyses of fibrous tourmalines from localities worldwide, several commonalities are apparent. Fibers typically nucleate on a preexisting substrate of tourmaline, but the fibers generally have a dramatically different composition than the substrate tourmaline. When fibers nucleate on a single tourmaline crystal, fibrous growth is restricted to the +c pole of the tourmaline. Tourmaline fibers also nucleate on or in other minerals without preexisting tourmaline. Most fibrous tourmalines form late in the paragenetic sequence of a geologic environment and generally where there is an open fluid-filled space, e.g., at the end of the tourmaline crystallization sequence in a pegmatite pocket or in a hydrous fluid-rich fracture system. Fibrous tourmaline compositions can be foititic, schorlitic, dravitic, or elbaitic, reflecting the dissolved components in the fluxing aqueous fluids. While some fibers are homogeneous, many fibers are chemically zoned with irregular, patchy, or oscillatory zoning, and the zoning tracks the chemical evolution trends in the host environment. Using newly derived expressions relating X-site cationic occupancy to aqueous fluid compositions, Na and Ca contents in aqueous fluids in local equilibrium with fibrous tourmaline suggest that in all petrologic settings fibrous tourmalines equilibrated with aqueous fluids having variable Na concentrations (0.07-0.48 mol/l Na with the lower ranges associated with foititic fibrous tourmaline) and with generally low Ca concentrations (,0.16 mol/l Ca). The fibrous tourmalines that have high oxy-species components are suggestive of formation in fluids with relatively high salinities. The compositions of fibrous tourmaline provide an additional method for deciphering the evolution of hydrothermal environments, particularly those associated with a dynamic fluid phase that is no longer present.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".