Letnikovite-(Ce), (Na□)Ca<sub>2</sub>Ce<sub>2</sub>[Si<sub>7</sub>O<sub>17</sub>(OH)]F<sub>4</sub>(H<sub>2</sub>O)<sub>4,</sub> a new mineral from the Darai-Pioz alkaline massif, Tajikistan: mineral description, crystal structure and a new single [Si<sub>7</sub>O<sub>17</sub>(OH)] sheet
Bibliographic record
Abstract
Abstract Letnikovite-(Ce), ideally (Na□)Ca 2 Ce 2 [Si 7 O 17 (OH)]F 4 (H 2 O) 4 , is a new mineral with no natural or synthetic analogues (IMA2022–132). The mineral occurs at the Darai-Pioz alkaline massif, Tien-Shan mountains, Tajikistan, in a silexite-like peralkaline pegmatite. Letnikovite-(Ce) occurs as isolated prismatic grains up to 0.03 × 0.1 mm in a quartz–pectolite aggregate. Associated minerals are quartz, fluorite, pectolite, baratovite, aegirine, leucosphenite, neptunite, reedmergnerite, orlovite, sokolovaite, mendeleevite-(Ce), odigitriaite, pekovite, zeravshanite, kirchhoffite and garmite. The mineral is colourless with a vitreous lustre and a white streak, and D calc. is 2.847 g/cm 3 . Letnikovite-(Ce) is monoclinic, C 2/ m , a = 7.4726(3), b = 22.9196(9), c = 13.9360(6) Å, β = 105.550(5)° and V = 2299.43(17) Å 3 . The chemical composition of letnikovite-(Ce) is SiO 2 42.38, Gd 2 O 3 0.16, Eu 2 O 3 0.28, Sm 2 O 3 0.07, Nd 2 O 3 5.64, Pr 2 O 3 1.69, Ce 2 O 3 11.73, La 2 O 3 2.24, PbO 1.22, SrO 5.77, FeO 0.32, CaO 11.87, MgO 1.14, Cs 2 O 0.57, K 2 O 0.65, Na 2 O 2.24, H 2 O 7.79, F 7.29, O = F –3.07, total 99.98 wt.%. The empirical formula calculated on 7 Si apfu is Na 0.72 K 0.14 Cs 0.04 Ca 2.10 Sr 0.55 Mg 0.28 Pb 0.05 Fe 0.04 (Ce 0.71 Nd 0.33 La 0.14 Pr 0.10 Eu 0.02 Gd 0.01 ) Σ1.31 Si 7 O 21.84 F 3.81 H 8.58 for Z = 4. The structural formula is (Na 0.72 Ca 0.16 □ 1.12 ) Σ2 (Cs 0.04 □ 0.96 ) Σ1 (Ca 1.83 □ 0.17 ) Σ2 (Mg 0.28 Fe 0.04 □ 0.68 ) Σ1 ( Ln 3+ 1.31 Sr 0.55 Ca 0.09 Pb 0.05 ) Σ2 [Si 7 O 17 (OH)]F 3.81 (H 2 O) 3.79 , where Ln 3+ 1.31 = (Ce 0.71 Nd 0.33 La 0.14 Pr 0.10 Eu 0.02 Gd 0.01 ) Σ1.31 . The simplified formula is (Na,□) 2 Ca 2 ( Ln 3+ ,Sr) 2 [Si 7 O 17 (OH)]F 4 (H 2 O) 4 , where Ce is the dominant lanthanoid. The crystal structure was solved by direct methods and refined to an R 1 index of 4.2%. In letnikovite-(Ce), the main structural unit is a layer which consists of the central heteropolyhedral Ca–Ce sheet and two adjacent single [Si 7 O 17 (OH)] sheets parallel to (001). In the Si–O–OH sheet, the Si tetrahedra form five-membered and ten-membered rings. This is the first occurrence of a single [Si 7 O 17 (OH)] 7– sheet in a mineral. The layers connect via Na and Cs at the interstitial A (1,2) sites, H 2 O groups and hydrogen bonding. The mineral is named in honour of Felix Artem'evich Letnikov (born October 3 rd ,1934) in recognition of his outstanding contributions to the field of petrology and geochemistry of Precambrian rocks.
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How this classification was reachedexpand
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 | 0.005 | 0.004 |
| Meta-epidemiology (narrow) | 0.012 | 0.010 |
| Meta-epidemiology (broad) | 0.010 | 0.005 |
| Bibliometrics | 0.003 | 0.010 |
| Science and technology studies | 0.005 | 0.006 |
| Scholarly communication | 0.008 | 0.006 |
| Open science | 0.008 | 0.007 |
| Research integrity | 0.007 | 0.009 |
| 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 itClassification
machine, unvalidatedMachine predicted; both teacher heads agree on what is shown here.
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".