The dumortierite supergroup. II. Three new minerals from the Szklary pegmatite, SW Poland: Nioboholtite, (Nb<sub>0.6</sub>□<sub>0.4</sub>)Al<sub>6</sub>BSi<sub>3</sub>O<sub>18</sub>, titanoholtite, (Ti<sub>0.75</sub>□<sub>0.25</sub>)Al<sub>6</sub>BSi<sub>3</sub>O<sub>18</sub>, and szklaryite, □Al<sub>6</sub>BAs<sup>3+</sup><sub>3</sub>O<sub>15</sub>
Bibliographic record
Abstract
Abstract Three new minerals in the dumortierite supergroup were discovered in the Szklary pegmatite, Lower Silesia, Poland. Nioboholtite, endmember (Nb0.6☐0.4)Al6B3Si3O18, and titanoholtite, endmember (Ti0.75☐0.25)Al6B3Si3O18, are new members of the holtite group, whereas szklaryite, endmember ☐Al6BAs3+3O15, is the first representative of a potential new group. Nioboholtite occurs mostly as overgrowths not exceeding 10 μm in thickness on cores of holtite. Titanoholtite forms patches up to 10 μm across in the holtite cores and streaks up to 5 μm wide along boundaries between holtite cores and the nioboholtite rims. Szklaryite is found as a patch ∼2 μm in size in As- and Sb- bearing dumortierite enclosed in quartz. Titanoholtite crystallized almost simultaneously with holtite and other Ta-dominant minerals such as tantalite-(Mn) and stibiotantalite and before nioboholtite, which crystallized simultaneously with stibiocolumbite during decreasing Ta activity in the pegmatite melt. Szklaryite crystallized after nioboholtite during the final stage of the Szklary pegmatite formation. Optical properties could be obtained only from nioboholtite, which is creamy-white to brownish yellow or grey-yellow in hand specimen, translucent, with a white streak, biaxial (–), nα = 1.740 – 1.747, nβ ∼ 1.76, nγ ∼ 1.76, and Δ < 0.020. Electron microprobe analyses of nioboholtite, titanoholtite and szklaryite give, respectively, in wt.%: P2O5 0.26, 0.01, 0.68; Nb2O5 5.21, 0.67, 0.17; Ta2O5 0.66, 1.18, 0.00; SiO2 18.68, 21.92, 12.78; TiO2 0.11, 4.00, 0.30; B2O3 4.91, 4.64, 5.44; Al2O3 49.74, 50.02, 50.74; As2O3 5.92, 2.26, 16.02; Sb2O3 10.81, 11.48, 10.31; FeO 0.51, 0.13, 0.19; H2O (calc.) 0.05, –, –, Sum 96.86, 96.34, 97.07, corresponding on the basis of O = 18–As–Sb to {(Nb0.26Ta0.02☐0.18)(Al0.27Fe0.05Ti0.01)☐0.21}Σ1.00Al6B0.92{Si2.03P0.02(Sb0.48As0.39Al0.07}Σ3.00(O17.09OH0.04☐0.87)Σ18.00, {(Ti0.32 Nb0.03 Ta0.03☐0.10)(Al0.35 Ti0.01 Fe0.01)☐0.15 }Σ1.00 Al6 B0.86 {Si2 . 3 6 (Sb0.5 1 As0.14 )}Σ3.01(O17.35☐0.65)Σ18.00 and {☐0.53 (Al0.41 Ti0.02 Fe0.02 )(Nb0.01☐0.01 )}Σ1.00Al6 B1.01 {(As1.07 Sb0.47 Al0.03 ) Si1.37 P0.06 }Σ3.00(O16.46☐1.54 )Σ18.00. Electron backscattered diffraction indicates that the three minerals are presumably isostructural with dumortierite, that is, orthorhombic symmetry, space group Pnma (no. 62), and unit-cell parameters close to a = 4.7001, b = 11.828, c = 20.243 Å, with V = 1125.36 Å3 and Z = 4; micro-Raman spectroscopy provided further confirmation of the structural relationship for nioboholtite and titanoholtite. The calculated density is 3.72 g/cm3 for nioboholtite, 3.66 g/cm3 for titanoholtite and 3.71 g/cm3 for szklaryite. The strongest lines in X-ray powder diffraction patterns calculated from the cell parameters of dumortierite of Moore and Araki (1978) and the empirical formulae of nioboholtite, titanoholtite and szklaryite are [d, Å, I (hkl)]: 10.2125, 67, 46, 19 (011); 5.9140, 40, 47, 57 (020); 5.8610, 66, 78, 100 (013); 3.4582, 63, 63, 60 (122); 3.4439, 36, 36, 34 (104); 3.2305, 100, 100, 95 (123); 3.0675, 53, 53, 50 (105); 2.9305, 65, 59, 51 (026); 2.8945, 64, 65, 59 (132), respectively. The three minerals have been approved by the IMA CNMNC (IMA 2012-068, 069, 070) and were named for their relationship to holtite and occurrence in the Szklary pegmatite, respectively.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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 source (direct Gemma or distilled Codex), 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".