FROM STRUCTURE TOPOLOGY TO CHEMICAL COMPOSITION. III. TITANIUM SILICATES: THE CRYSTAL CHEMISTRY OF BARYTOLAMPROPHYLLITE
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Bibliographic record
Abstract
The crystal structure of barytolamprophyllite, ideally (BaK) Na 3 Ti 3 (Si 2 O 7 ) 2 O 2 (OH) 2 , a 19.8971(7), b 7.1165(3), c 5.4108(2) A, β 96.676(2)°, V 760.96(3) A 3 , space group C 2/ m , Z = 2, D calc. 3.521 g.cm −3 , from Mt. Yuksporr, Khibina alkaline massif, Kola Peninsula, Russia, has been refined to R 1 = 2.82% on the basis of 1175 unique reflections ( F o > 4σ F ) collected on a Bruker AXS SMART APEX diffractometer with a CCD detector and Mo K α radiation. An electron-microprobe analysis gave (wt.%): SiO 2 29.31, Al 2 O 3 0.16, Nb 2 O 5 0.11, TiO 2 28.39, Fe 2 O 3 0.49, FeO 2.66, MnO 2.42, MgO 0.26, CaO 0.88, SrO 4.11, BaO 16.37, K 2 O 3.52, Na 2 O 7.90, F 1.69, H 2 O 0.77 (calculated from structure refinement), O=F −0.71, for a total of 98.33. The empirical formula is (Ba 0.88 K 0.61 Sr 0.33 Ca 0.05 □ 0.13 ) ∑2.00 (Na 2.09 Fe 2+ 0.30 Mn 2+ 0.28 Ca 0.08 Mg 0.05 □ 0.20 ) ∑3.00 (Ti 2.91 Fe 3+ 0.05 Al 0.03 Nb 0.01 ) ∑3.00 (Si 2 O 7 ) 2 O 2 [F 0.73 (OH) 0.70 O 0.57 ] ∑2.00 , Z = 2, calculated on the basis of 4 Si apfu . The crystal structure of barytolamprophyllite can be described as a combination of two blocks, a TS (titanium silicate) block and an I (intermediate) block. The TS block consists of HOH sheets (H heteropolyhedral, O octahedral), which occur in 24 Ti disilicate minerals. In the TS block, there are six cation sites, a [4]-coordinated Si site with = 1.631 A, two Ti-dominant sites, the [5]-coordinated M H site and [6]-coordinated M °(1) site, and two [6]-coordinated Na-dominant sites, M °(2) and M °(3). The M H site (= Ti 1.97 Al 0.03 pfu ) is coordinated by five O atoms, with H –O> = 1.914 A; the M °(1) site (= Ti 0.94 Fe 3+ 0.05 Nb 0.01 pfu ) is coordinated by four O atoms and two OH groups, with = 1.993 A; the M °(2) and M °(3) sites (= Na 1.00 and Na 1.09 Fe 2+ 0.30 Mn 2+ 0.28 Ca 0.08 Mg 0.05 □ 0.20 pfu , respectively) are coordinated by six O atoms with = 2.441 A, and four O atoms and two OH groups, with = 2.296 A, respectively. The M H square pyramid and (Si 2 O 7 ) groups constitute the H sheet. The M°(1–3) octahedra form the close-packed O sheet. Linkage of H and O sheets occurs via common vertices of M H square pyramids and (Si 2 O 7 ) groups with M°(1–3) octahedra. The second or intermediate I block includes the [10]-coordinated A P site (= Ba 0.88 K 0.61 Sr 0.33 Ca 0.05 □ 0.13 pfu ) with A P –O> = 2.843 A. The TS block and the I block (which ideally is a layer of Ba and K atoms) alternate along a . The ideal formula of barytolamprophyllite is (BaK) Na 3 Ti 3 (Si 2 O 7 ) 2 O 2 (OH) 2 , Z = 2. The topology of its structure is identical to that of lamprophyllite, (SrNa) Na 3 Ti 3 (Si 2 O 7 ) 2 O 2 (OH) 2 , and nabalamprophyllite, Ba Na Na 3 Ti 3 (Si 2 O 7 ) 2 O 2 (OH) 2 . We explain why, for lamprophyllite, barytolamprophyllite and nabalamprophyllite, the chemical composition of the I block is of the form (A 2+ A + ) with a total charge of 3+, and the ideal formula of the minerals is (A 2+ A + ) Na 3 Ti 3 (Si 2 O 7 ) 2 O 2 (OH) 2 , where A 2+ = Sr 2+ , Ba 2+ , Ca 2+ ; A + = Na + , K + .
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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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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