BRONTESITE, (NH4)3PbCl5, A NEW PRODUCT OF FUMAROLIC ACTIVITY FROM LA FOSSA CRATER, VULCANO, AEOLIAN ISLANDS, ITALY
Bibliographic record
Abstract
The new mineral species brontesite , ammonium lead chloride (NH 4 ) 3 PbCl 5 , was found in a medium-temperature (~250°C) active fumarole at La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy. The mineral occurs on a pyroclastic breccia as colorless to white tabular crystals up to 0.1 mm in length, in association with bismuthinite, godovikovite, demicheleite-(Cl), demicheleite-(Br), alunite, IMA 2008–057, (NH 4 ) 4 NaAl 2 (SO 4 ) 4 Cl(OH) 2 , and IMA 2009–049, BiSI. The mineral is orthorhombic, space group Pnma (no. 62), with Z = 4; the unit-cell parameters are: a 8.434(1), b 15.759(2), c 8.462(1) A, V 1124.7(2) A 3 . The strongest six reflections in the X-ray powder-diffraction pattern [ d obs in A( I )( hkl) ] are: 3.067(100)(132), 2.020(80)(342), 2.710(78)(241), 1.910(78)(134), 2.421(75)(152) and 1.491(75)(373). Chemical analyses made with an electron microprobe in EDS mode gave, on average, Pb 47.8, Cl 36.1, Br 3.7, K 1.1, NH 4 11.3 (by difference), for a total of 100.0 wt.%, corresponding to the empirical formula: [(NH 4 ) 2.87 K 0.13 ] ∑3.00 Pb 1.09 (Cl 4.79 Br 0.21 ) ∑5.00 . The measured density is 2.72(1) g/cm 3 . The average index of refraction n is 1.70(3) (λ = 589 nm). Using single-crystal diffraction data, the structure was refined to a final R = 0.0238 for 1463 independent observed reflections [ I > 2σ( I )]. The coordination polyhedron of the independent eight-coordinated Pb atom is a bicapped trigonal prism with Pb–Cl distances ranging from 2.777(1) to 3.724(1) A. The Pb polyhedra are connected by sharing edges to form chains running along [100]. There are also two independent sites occupied by ammonium ions whose environment corresponds nearly exactly to that of the Rb atoms in Rb 3 PbCl 5 . It is essentially similar to that of the lead atom, i.e. , the chlorine atoms are also arranged at the corners of bicapped trigonal prisms. There is some substitutional disorder involving the Pb 2+ and NH 4 + ions, similar to that occurring for Pb 2+ and K + in the high-temperature modification of KPb 2 Cl 5 . The mineral was approved as a new species by the IMA Commission on New Minerals, Nomenclature and Classification (IMA #2008–014); it is named after Brontes (Bρο′ντης), one of the three Cyclops (Kν′κλωπeς) and a son of Uranus.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 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 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".