Tamuraite, Ir5Fe10S16, a New Species of Platinum-Group Mineral from the Sisim Placer Zone, Eastern Sayans, Russia
Bibliographic record
Abstract
Tamuraite, ideally Ir5Fe10S16, occurs as discrete phases (≤20 μm) in composite inclusions hosted by grains of osmium (≤0.5 mm across) rich in Ir, in association with other platinum-group minerals in the River Ko deposit of the Sisim Placer Zone, southern Krasnoyarskiy Kray, Russia. In droplet-like inclusions, tamuraite is typically intergrown with Rh-rich pentlandite and Ir-bearing members of the laurite–erlichmanite series (up to ~20 mol.% “IrS2”). Tamuraite is gray to brownish gray in reflected light. It is opaque, with a metallic luster. Its bireflectance is very weak to absent. It is nonpleochroic to slightly pleochroic (grayish to light brown tints). It appears to be very weakly anisotropic. The calculated density is 6.30 g·cm−3. The results of six WDS analyses are Ir 29.30 (27.75–30.68), Rh 9.57 (8.46–10.71), Pt 1.85 (1.43–2.10), Ru 0.05 (0.02–0.07), Os 0.06 (0.03–0.13), Fe 13.09 (12.38–13.74), Ni 12.18 (11.78–13.12), Cu 6.30 (6.06–6.56), Co 0.06 (0.04–0.07), S 27.23 (26.14–27.89), for a total of 99.69 wt %. This composition corresponds to (Ir2.87Rh1.75Pt0.18Ru0.01Os0.01)Σ4.82(Fe4.41Ni3.90Cu1.87Co0.02)Σ10.20S15.98, calculated based on a total of 31 atoms per formula unit. The general formula is (Ir,Rh)5(Fe,Ni,Cu)10S16. Results of synchrotron micro-Laue diffraction studies indicate that tamuraite is trigonal. Its probable space group is R3m (#166), and the unit-cell parameters are a = 7.073(1) Å, c = 34.277(8) Å, V = 1485(1) Å3, and Z = 3. The c:a ratio is 4.8462. The strongest eight peaks in the X-ray diffraction pattern [d in Å(hkl)(I)] are: 3.0106(216)(100), 1.7699(420)(71), 1.7583(2016)(65), 2.7994(205)(56), 2.9963(1010)(50), 5.7740(102)(45), 3.0534(201)(43) and 2.4948(208)(38). The crystal structure is derivative of pentlandite and related to that of oberthürite and torryweiserite. Tamuraite crystallized from a residual melt enriched in S, Fe, Ni, Cu, and Rh; these elements were incompatible in the Os–Ir alloy that nucleated in lode zones of chromitites in the Lysanskiy layered complex, Eastern Sayans, Russia. The name honors Nobumichi Tamura, senior scientist at the Advanced Light Source of the Lawrence Berkeley National Laboratory, Berkeley, California.
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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 | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| 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 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".