FROM STRUCTURE TOPOLOGY TO CHEMICAL COMPOSITION. XV. TITANIUM SILICATES: REVISION OF THE CRYSTAL STRUCTURE AND CHEMICAL FORMULA OF SCHÜLLERITE, Na<sub>2</sub>Ba<sub>2</sub>Mg<sub>2</sub>Ti<sub>2</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>O<sub>2</sub>F<sub>2</sub>, FROM THE EIFEL VOLCANIC REGION, GERMANY
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Bibliographic record
Abstract
The crystal structure of schullerite, ideally Na 2 Ba 2 Mg 2 Ti 2 (Si 2 O 7 ) 2 O 2 F 2 , a 5.396(1), b 7.071(1), c 10.226(2) A, α 99.73(3), β 99.55(3), γ 90.09(3)°, V 379.1(2) A 3 , Z = 1, from the Eifel volcanic region, Germany, has been refined in the space group P 1 to R = 1.33% using 2247 observed ( F o > 4σ F ) reflections collected with a single-crystal Bruker D8 three-circle diffractometer equipped with a rotating-anode generator (Mo K α radiation), multilayer optics and an APEX-II detector. The empirical formula for schullerite was calculated on the basis of 18 (O + F) anions: (Na 1.10 Ca 0.43 Mn 0.30 Fe 2+ 0.17 ) ∑2 (Ba 1.57 Sr 0.14 K 0.14 □ 0.15 ) ∑2 (Mg 0.79 Fe 2+ 0.71 Na 0.33 Fe 3+ 0.17 ) ∑2 (Ti 1.67 Fe 3+ 0.21 Nb 0.09 Zr 0.02 Al 0.01 ) ∑2 Si 3.95 O 15.93 F 2.07 , D calc. = 3.879 g/cm 3 , Z = 1, with Fe 3+ / (Fe 2+ +Fe 3+ ) ratio determined by Mossbauer spectroscopy. Schullerite is a Group-IV TS-block mineral: Ti + Mg = 4 apfu . The crystal structure of schullerite is an alternation of TS (Titanium Silicate) and I (intermediate) blocks of the ideal composition [Na 2 Mg 2 Ti 2 (Si 2 O 7 ) 2 O 2 F 2 ] 4− and [Ba 2 ] 4+ , respectively. The TS block is composed of the central O (octahedral) sheet and two adjacent H (heteropolyhedral) sheets. In the O sheet, there are two brookite-like chains of M O octahedra of the following ideal compositions: [Mg 2 O 8 ] 12− [M O (1)] and [Na 2 O 8 ] 14− [M O (2)]; the ideal composition of the O sheet is [Na 2 Mg 2 O 2 F 2 ] 0. The H sheet is composed of the [5]-coordinated Ti-dominant M H polyhedra and Si 2 O 7 groups; the composition of the two H sheets is [Ti 2 (Si 2 O 7 ) 2 ] 4−. In schullerite, the TS block has a topology characteristic of Group IV of TS-block minerals: two H sheets connect to the O sheet such that two Si 2 O 7 groups link to the Mg-dominant octahedra of the O sheet adjacent along t 1 . In the O sheet, occurrence of divalent cations at the M O (1) site results in the presence of monovalent anions, F − , at the X O A site. The A P site of the H sheet is occupied mainly by Ba; the A P site is shifted from the plane of the H sheet, and Ba atoms constitute the I block of the composition [Ba 2 ] 4+ . Schullerite is the only mineral of Group IV that has (1) a brookite-like [Mg 2 O 8 ] 12− chain of octahedra in the O sheet; (2) [5]-coordinated Ti in the H sheet; (3) Ba atoms in the I block. The ideal structural formula of schullerite is of the form A P 2 M H 2 M O 4 (Si 2 O 7 ) 2 (X O M ) 2 (X O A ) 2 : Ba 2 Ti 2 Na 2 Mg 2 Ti 2 (Si 2 O 7 ) 2 O 2 F 2 , Z = 1.
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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 | 0.003 | 0.002 |
| Meta-epidemiology (narrow) | 0.007 | 0.006 |
| Meta-epidemiology (broad) | 0.007 | 0.003 |
| Bibliometrics | 0.002 | 0.005 |
| Science and technology studies | 0.005 | 0.009 |
| Scholarly communication | 0.003 | 0.003 |
| Open science | 0.009 | 0.004 |
| Research integrity | 0.006 | 0.007 |
| Insufficient payload (model declined to judge) | 0.000 | 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 it