Nacareniobsite-(Nd), Ca2(CaNd)Na3Nb(Si2O7)2(OF)F2, a New Rinkite-Group (Seidozerite-Supergroup) Mineral from the Darai-Pioz Alkaline Massif, Tajikistan: Description and Crystal Structure
Bibliographic record
Abstract
Abstract Nacareniobsite-(Nd), Ca2(CaNd)Na3Nb(Si2O7)2(OF)F2, is a new rinkite-group (seidozerite-supergroup) TS-block mineral from the Darai-Pioz alkaline massif, Tien-Shan mountains, Tajikistan. It occurs as prismatic isolated grains up to 0.3 mm long and 0.03 mm thick in a quartz-pectolite aggregate in a silexite-like peralkaline pegmatite. Associated minerals are reedmergnerite, leucosphenite, baratovite, aegirine, orlovite, sokolovaite, mendeleevite-(Ce), odigitriaite, pekovite, zeravshanite, kirchhoffite, fluorite, and garmite. Crystals are colorless and transparent with a vitreous luster. Nacareniobsite-(Nd) has a white streak and uneven fracture and does not fluoresce under cathode or ultraviolet light. Cleavage is very good on {100}, no parting was observed, Mohs hardness is 5, and it is brittle, Dmeas. = 3.58(2), Dcalc. = 3.608 g/cm3. It is optically biaxial (+) with refractive indices α = 1.664(2), β = 1.670(2), γ = 1.692(2); 2Vcalc. = 56°. Nacareniobsite-(Nd) is monoclinic, space group P21/c, a = 7.4195(15), b = 5.6567(11), c = 18.788(4) Å, β = 101.38(3)°, V = 773.0(3) Å3. The six strongest reflections in the X-ray powder-diffraction data [d(Å), I, (h k l)] are: 3.059, 100, (0 0 6, −2 1 2, 2 1 0); 2.928, 36, (2 1 1, −2 1 3); 2.688, 27, (1 1 5, 0 1 6); 1.847, 23, (−4 0 2, 2 1 7, −2 1 9); 2.782, 21, (0 2 1); 1.674, 19, (−2 3 1). The empirical formula calculated on 18 (O + F) is Na2.98Ca2.79Sr0.27Y0.17(Nd0.32Ce0.26Sm0.07Pr0.05La0.04Gd0.04Tb0.01Dy0.01Tm0.01Lu0.01Ho0.01Eu0.01Er0.01Yb0.01)Σ0.86(Nb0.87Ti0.10)Σ0.97(Si4.01O14)O1.00 F3.00,Z = 2. The crystal structure was refined to R1 = 3.85% on the basis of 2409 unique reflections (FO > 4σ|F|) and is a framework of TS (Titanium-Silicate) blocks. The TS block consists of HOH sheets (H – heteropolyhedral, O – octahedral) parallel to (100). In the O sheet, the [6]MO(1), [8]MO(2), and [6]MO(3) sites ideally give Nb, Na, and Na2apfu, cations of the O sheet sum to Na3Nb apfu. In the H sheet, the [7]MH and [7]AP sites are occupied by Ca1.30(Ln0.53Y0.17)Σ0.70 and Ca1.16Sr0.27Na0.24Ln0.33apfu, ideally (CaNd) and Ca2apfu. The AP + MH sites ideally give Ca2(CaNd) apfu. The MH and AP polyhedra and Si2O7 groups constitute the H sheet. Linkage of H and O sheets via common vertices of MO(1–3), MH and AP polyhedra, and Si2O7 groups results in a TS block. In the structure, TS blocks link via common edges of MH and AP polyhedra and common vertices of MH, AP, and Si polyhedra of the H sheets belonging to two TS blocks. For nacareniobsite-(Nd), the ideal structural formula of the form AP2MH2MO4(Si2O7)2(XOM)2(XOA)2 is Ca2(CaNd)Na3Nb(Si2O7)2(OF)F2. The mineral is structurally identical to nacareniobsite-(Y), Ca2(CaY)Na3Nb(Si2O7)2(OF)F2, and nacareniobsite-(Ce), Ca2(CaCe)Na3Nb(Si2O7)2(OF)F2.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".