The Effect of Crystal Orientation on <i>In Situ</i> Rb‐Sr Mica Geochronology
Bibliographic record
Abstract
Mica crystals have a highly asymmetric structure, arranged in sheets of two tetrahedral layers bonded to a single octahedral layer. The individual sheets are only weakly bonded, leading to perfect basal cleavage. The recent proliferation of in situ laser ablation‐based Rb‐Sr geochronology of mica makes it critical to understand if orientation of the crystal lattice relative to the laser beam may impart a differential ‘matrix’ effect on Rb‐Sr ratios during ablation. Analyses of mica crystals from eight different samples, including biotite, muscovite and phlogopite, mounted with their c ‐axes approximately parallel (flat‐mounted) and perpendicular (vertically mounted) to the incident laser beam, result in dates that are statistically indistinguishable. Moreover, and consistent with previous work, analysis of vertically mounted crystals generally resulted in less within‐spot variation in 87 Rb/ 86 Sr, and is, therefore, the recommended orientation for Rb‐Sr geochronology measurements, where practical.
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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 | 0.002 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| 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) | 0.001 | 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".