The Precious Opal Deposit At Wegel Tena, Ethiopia: Formation<i>Via</i>Successive Pedogenesis Events
Bibliographic record
Abstract
Abstract Since its discovery in 2008, the opal deposit in the Wegel Tena area of Ethiopia, located within an Oligocene ignimbritic trap, has become a major provider of precious opal. This study provides new field evidence and laboratory results that reinforce the pedogenetic model for gem opal formation. In the eight mines investigated, opal occurs in lenticular horizons within an unwelded ignimbrite bed. Moreover, several deposits are superimposed in the sequence, indicating that gem opal formation occurred several times in the same place. We observed that, in contrast to the other beds, the opal-bearing horizons are strongly weathered: volcanic glass is altered to smectite, rocks with a granular microstructure are apparent, and cavities are covered by illuvial clays. These features are typical of pedogenetic processes. Plant fossils in the opals reveal a well preserved cellular structure composed of chalcedony. These observations are consistent over all the mines, supporting the pedogenetic model for precious opal formation in the Wegel Tena area.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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 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".