From structure topology to chemical composition. XX. Titanium silicates: the crystal structure of hejtmanite, Ba<sub>2</sub>Mn<sub>4</sub>Ti<sub>2</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>O<sub>2</sub>(OH)<sub>2</sub>F<sub>2</sub>, a Group-II TS-block mineral
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Bibliographic record
Abstract
Abstract The crystal structure of hejtmanite, Ba 2 Mn 4 Ti 2 (Si 2 O 7 ) 2 O 2 (OH) 2 F 2 , from Mbolve Hill, Mkushi River area, Central Province, Zambia (holotype material) has been refined on a twinned crystal to R 1 = 1.88% on the basis of 4539 [|F| > 4|F|] reflections. Hejtmanite is triclinic, C 1̅, a = 10.716(2), b = 13.795(3), c = 11.778 (2) , = 90.07(3), = 112.24(3), = 90.03(3), V = 1612(2) 3 . Chemical analysis (electron microprobe) gives: Ta 2 O 5 0.09, Nb 2 O 5 1.27, ZrO 2 0.65, TiO 2 14.35, SiO 2 23.13, BaO 26.68, SrO 0.19, FeO 11.28, MnO 15.12, Cs 2 O 0.05, K 2 O 0.33, F 3.82, H 2 O calc . 1.63, O = F 1.61, total 97.10 wt.%, where the H 2 O content was calculated from the crystal-structure refinement, with (OH F) = 4 apfu. The empirical formula, calculated on the basis of 20 (O F) anions, is of the form (Si 2 O 7 ) 2 (X O ) 4 (X P ) 2 , Z=4: (Ba 1.82 K 0.07 Sr 0.02 ) Σ1.91 (Mn 2.33 Zr 0.04 Mg 0.03 ) Σ3.95 (Ti 1.88 Nb 0.10 Zr 0.02 ) Σ2 (Si 2.02 O 7 ) 2 O 2 [(OH) 1.89 F 0.11 ] Σ2 F 2 . The crystal structure is a combination of a TS (Titanium Silicate) block and an I (intermediate) block. The TS block consists of HOH sheets (H heteropolyhedral, O octahedral). The topology of the TS block is as in Group-II TS-block minerals: Ti ( Nb) = 2 apfu per (Si 2 O 7 ) 2 [as defined by Sokolova (2006)]. In the O sheet, five [6] M O sites are occupied mainly by Mn, less Fe 2 and minor Zr and Mg, with <MOφ> = 2.198 (φ = O,OH), ideally giving Mn 4 apfu. In the H sheet, two [6] M H sites are occupied mainly by Ti, with <M H φ> = 1.962 (φ = O,F), ideally giving Ti 2 apfu; four [4] Si sites are occupied by Si, with < SiO> = 1.625 . The M H octahedra and Si 2 O 7 groups constitute the H sheet. The two [12] Ba-dominant A P (1,2) sites, with <A P φ> = 2.984 (φ = O, F), ideally give Ba 2 apfu. Two (1,2) and two (1,2) sites are occupied by O atoms and OH groups with minor F, respectively, ideally giving (X O ) 4 = ( ) 2 ( )2=O 2 (OH) 2 pfu. Two (1,2) sites are occupied by F, giving F 2 apfu. TS blocks link via a layer of Ba atoms which constitute the I block. Simplified and end-member formulae of hejtmanite are Ba 2 (Mn,Fe 2 ) 4 Ti 2 (Si 2 O 7 ) 2 O 2 (OH,F) 2 F 2 and Ba 2 Mn 4 Ti 2 (Si 2 O 7 ) 2 O 2 (OH) 2 F 2 , Z = 4. Hejtmanite is a Mn-analogue of bafertisite, Ba 2 4 Ti 2 (Si 2 O 7 ) 2 O 2 (OH) 2 F 2 .
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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 | 0.004 | 0.004 |
| Meta-epidemiology (narrow) | 0.012 | 0.010 |
| Meta-epidemiology (broad) | 0.012 | 0.006 |
| Bibliometrics | 0.005 | 0.011 |
| Science and technology studies | 0.005 | 0.010 |
| Scholarly communication | 0.003 | 0.006 |
| Open science | 0.011 | 0.007 |
| Research integrity | 0.009 | 0.010 |
| Insufficient payload (model declined to judge) | 0.001 | 0.003 |
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