Dukeite, Bi <sub>24</sub> <sup>3+</sup> Cr <sub>8</sub> <sup>6+</sup> O <sub>57</sub> (OH) <sub>6</sub> (H <sub>2</sub> O) <sub>3</sub> , a new mineral from Brejaúba, Minas Gerais, Brazil: Description and crystal structure
Bibliographic record
Abstract
Dukeite, Bi 3+ 24 Cr 8 6+ O 57 (OH) 6 (H 2 O) 3 , space group P31c, a = 15.067(3), c = 15.293(4) Å, V = 3007(1) Å 3 , Z = 2, is a new mineral found on a museum specimen labeled as originating from the São José Mine, Brejaúba, Minas Gerais, Brazil. The strongest seven lines of the X-ray powder-diffraction pattern [d in Å (I) (hkl)] are: 7.650 (50) (002), 3.812 (40) (004), 3.382 (100) (222), 2.681 (70) (224), 2.175 (40) (600), 2.106 (40) (226), 1.701 (50) (228). It occurs as groupings of tightly bound 1 × 0.3 mm2 sized sheaves that are associated with pucherite, schumacherite, bismutite, and hechtsbergite. Individual acicular crystals do not exceed 100 μm in length by 1-2 μm in width. Crystals are yellow inclining to a dirty yellow-brown, possess a bright yellow streak, are transparent, brittle, resinous, and do not fluoresce under ultraviolet light. The estimated Mohs hardness is between 3 and 4, the calculated density (for the empirical formula) is 7.171 g/cm 3 , and the mineral is slowly soluble in concentrated HCl. Electron-microprobe analyses yielded Bi 2 O 3 85.06, CrO 3 11.65, V 2 O 5 0.59, H 2 O (calc.) [1.67], total [98.97] wt%. The empirical formula, derived from the crystalstructure analysis and electron-microprobe analyses, is Bi 3+ 23.95 (Cr 6+ 7.64 V 5+ 0.43 )Σ 8.07 O 56.84 (OH) 6.16 ⋅3.01 H 2 O, based on O = 66. In reflected plane-polarized light in air it is gray to purplish gray with strong yellow internal reflections. Bireflectance is very weak. Measured reflectance values, in air and in oil, are tabulated: indices of refraction calculated from these at 590 nm are 2.33 and 2.37. The name honors Duke University, Durham, North Carolina, in whose collection the mineral was found and also recognizes the contribution of the Duke family to the advancement of scientific knowledge. The crystal structure of dukeite was solved by direct methods and refined on the basis of F 2 using all unique reflections measured with MoKα X-radiation on a CCD-equipped diffractometer. The final R1 index was 8.7%, calculated using 1033 observed reflections. It contains irregular layers of Biφn polyhedra (φ: O, OH-, H 2 O) parallel to (001), separated and connected by CrO 4 tetrahedra to form a framework structure. One CrO 4 tetrahedron shares all of its vertices with Biφn polyhedra, whereas the other three CrO 4 tetrahedra share only three vertices each with the Biφn polyhedra on either side
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".