Micro- and nano-size hydrogarnet clusters in calcium silicate garnet: Part II. Mineralogical, petrological, and geochemical aspects
Bibliographic record
Abstract
Abstract The nominally anhydrous, calcium-silicate garnets, grossular (Ca3Al2Si3O12), andradite (Ca3Fe23+Si3O12), schorlomite (Ca3Ti24+[Si,Fe23+]O12), and their solid solutions can incorporate structural OH-, often termed “water.” The IR single-crystal spectra of several calcium silicate garnets were recorded between 3000 and 4000 cm–1. Spectroscopic results are also taken from the literature. All spectra show various OH- stretching modes between 3500 and 3700 cm–1 and they are analyzed. Following the conclusions of Part I of this study, the garnets appear to contain local microscopic- and nano-size Ca3Al2H12O12- and Ca3Fe23+H12O12-like domains and/or clusters dispersed throughout an anhydrous “matrix.” The substitution mechanism is the hydrogarnet one, where (H4O4)4– ↔ (SiO4)4–, and various local configurations containing different numbers of (H4O4)4– groups define the cluster type. A single (H4O4) group is roughly 3 Å across and most (H4O4)-clusters are between this and 15 Å in size. This model can explain the IR spectra and also other experimental results. Various hypothetical “defect” and cation substitutional mechanisms are not needed to account for OH- incorporation and behavior in garnet. New understanding at the atomic level into published dehydration and H-species diffusion results, as well as H2O-concentration and IR absorption-coefficient determinations, is now possible for the first time. End-member synthetic and natural grossular crystals can show similar OH- “band patterns,” as can different natural garnets, indicating that chemical equilibrium could have operated during their crystallization. Under this assumption, the hydrogarnet-cluster types and their concentrations can potentially be used to decipher petrologic (i.e., P-T-X) conditions under which a garnet crystal, and the rock in which it occurs, formed. Schorlomites from phonolites contain no or very minor amounts of H2O (0.0 to 0.02 wt%), whereas Ti-bearing andradites from chlorite schists can contain more H2O (∼0.3 wt%). Different hydrogarnet clusters and concentrations can occur in metamorphic grossulars from Asbestos, Quebec, Canada. IR absorption coefficients for H2O held in hydrogrossularand hydroandradite-like clusters should be different in magnitude and this work lays out how they can be best determined. Hydrogen diffusion behavior in garnet crystals at high temperatures is primarily governed by the thermal stability of the different local hydrogarnet clusters at 1 atm.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.002 |
| 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 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".