Relative humidity as a driver of structural change in three new ferric-sulfate-tellurite hydrates: New minerals tamboite and metatamboite, and a lower-hydrate derivative, possibly involving direct uptake of atmospheric {H2O}4 clusters
Bibliographic record
Abstract
Abstract Tamboite (x = 3; y = 2) and metatamboite (x = 3; y = 0), Fe3+3(SO4)(Te4+O3)3(Te4+O(OH)2)(OH)(H2O)x{H2O}y, are new tellurite minerals from the Tambo mine, Coquimbo Province, Chile. The two minerals transform to each other reversibly with changes in ambient humidity. They occur as pale-yellow clusters of radiating fiber bundles on the surface of a compact aggregate of silicified tuff. Tamboite and metatamboite are optically biaxial, and their calculated mean index of refraction is greater than 1.80. The calculated densities are 3.648 g/cm3 for tamboite and 4.053 g/cm3 for metatamboite. Tamboite and metatamboite are monoclinic, space group P21/c, Z = 4. Unit-cell parameters for tamboite are a 16.879(10), b 7.310(4), c 16.666(9) Å, β 108.857(11)°, V 1958(3) Å3; for metatamboite they are a 14.395(5), b 7.296(4), c 16.411(6) Å, β 98.909(10)°, V 1703(2) Å3. Chemical analysis by electron microprobe gave the empirical cations [calculated on the basis of 22 anions pfu with OH = 3 and H2O = 5 pfu (tamboite) or H2O = 3 pfu (metatamboite)] as (Fe3+3.10Al0.15)Σ3.25(S6+0.75Se6+0.05)Σ0.80Te4+4.11. The seven strongest lines in the X-ray powder diffraction patterns [listed as d (Å), I, (hkl)] are as follows: metatamboite: 14.221, 100, (100); 2.874, 13, ; 3.140, 12, (221); 3.423, 11, ; 3.400, 11, (312); 3.012, 11, ; 4.054, 9, ; tamboite: 16.068, 100, (100); 3.425, 9, ; 2.999, 8, ; 3.171, 6, (221); 2.853, 5, ; 4.153, 4, ; 3.943, 4, (004). The crystal structures were solved by direct methods and refined to R1 indices of 4.3 and 3.0%. The structures consist of virtually identical ferric-sulfate-tellurite-hydrate slabs that are constructed from strands of ferric-sulfate-hydrate polyhedra linked by Te4+ cations. In metatamboite, the slabs are linked directly by hydrogen bonds whereas in tamboite, interslab linkage occurs by hydrogen bonds through interstitial {H2O}4 clusters known as Ci cyclic tetramers. Exposure of a crystal to a desiccant at room temperature resulted in a third variant (x = 2; y = 0) with the structural formula Fe3+2Fe2+(SO3(OH))(Te4+O3)3(Te4+O(OH)2)(OH)(H2O)x, space group P21/c, Z = 4, a 16.879(10), b 7.310(4), c 16.666(9) Å, β 108.857(11)°, V 1958(3) Å3, calculated density 4.176 g/cm3. This lower-hydrate variant has less cation-bonded (H2O) than metatamboite and tamboite, and the ferric-sulfate-tellurite-hydrate slabs are polymerized to form a framework structure. Attempts to transform the lower hydrate back to tamboite or metatamboite at room temperature and elevated humidity were unsuccessful.
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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 | 0.000 | 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".