BRONTESITE, (NH4)3PbCl5, A NEW PRODUCT OF FUMAROLIC ACTIVITY FROM LA FOSSA CRATER, VULCANO, AEOLIAN ISLANDS, ITALY
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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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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) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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 it