DEMARTINITE, A NEW POLYMORPH OF K2SiF6 FROM LA FOSSA CRATER, VULCANO, AEOLIAN ISLANDS, ITALY
Bibliographic record
Abstract
Demartinite, ideally K 2 SiF 6 , is a new hexagonal polymorph of potassium fluorosilicate, found in a fumarole at the rim of La Fossa crater, Vulcano Island, Aeolian Archipelago, Sicily, Italy. The mineral occurs as colorless hexagonal pyramidal crystals up to 0.3 mm across on a fragment of altered pyroclastic breccia, together with hieratite, avogadrite and knasibfite, a recently approved tetrafluoroborate-hexafluorosilicate of Na and K. The mineral is hexagonal (6 mm ), space group P 6 3 mc , with a 5.6461(8) and c 9.2322(18) A, V 254.88(7) A 3 . The crystals are sharp hexagonal pyramids {112}, terminated by the {001} pedion. The crystal structure has been refined to a final R index of 0.018; its SiF 6 2− groups have the same geometry as in the other natural fluorosilicates known. There are two independent twelve-coordinated K sites, displaying distorted cuboctahedral and hexagonal cuboctahedral coordination, respectively. The K–F distances are in the range 2.800(2) – 3.087(2) A, with an average of 2.885 A. The Si–F distances in the octahedral SiF 6 2− anion range from 1.681(2) to 1.689(2) A, with an average of 1.685 A. The chemical analysis obtained by EDS microprobe gave (wt%) K 35.1, Si 12.4, F 51.0, Na 0.2, total 98.7, corresponding to the empirical formula (K 2.00 Na 0.02 ) ∑2.02 Si 0.99 F 5.99 , based on nine atoms per formula unit. The calculated density is 2.87 g cm −3 , the measured density obtained by flotation in heavy liquids is 2.85 g cm −3 . The indices of refraction are: ω 1.350 ± 0.005; e 1.340 ± 0.005 (589 nm). Demartinite is uniaxial (−) and nonpleochroic (colorless). The strongest six lines in the X-ray powder-diffraction pattern [ d obs in A(I) hkl ] are: 2.301(100)(004), 4.62(75)(002), 2.155(54)(022), 4.32(43)(011), 4.90(25)(010) and 2.358(22)(021). The mineral is named in honor of Prof. Francesco Demartin (b. 1953), who has made significant contributions to the chemistry of metallic clusters and to the crystal structure of Alpine rare-earth minerals and uranium minerals. Both the mineral and the mineral name have been approved by the Commission on New Minerals and Mineral Names of the IMA (No. 2006–034).
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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) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".