THE CRYSTAL STRUCTURE OF VLADIMIRITE, WITH A REVISED CHEMICAL FORMULA, Ca4(AsO4)2(AsO3OH){middle dot}4H2O
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Bibliographic record
Abstract
Two samples of vladimirite, one from Bou Azzer, Morocco, and the other from a new occurrence in Copiapo, Chile (designated as R100075 and R080001, respectively), were examined with an electron microprobe, single-crystal X-ray diffraction, and Raman spectroscopy. Our results show that vladimirite is monoclinic with space group P 2 1 / c and unit-cell parameters a 5.8279(2), b 10.1802(4), c 22.8944(10) A, β 96.943(2)°, and V 1348.35(9) A 3 for R100075 and a 5.8220(1), b 10.1750(2), c 22.8816(6) A, β 96.902(1)°, and V 1345.66(5) A 3 for R080001. The structure determinations, with R 1 = 0.022 and 0.023 for R100075 and R080001, respectively, yielded an ideal chemical formula Ca 4 (AsO 4 ) 2 (AsO 3 OH)·4H 2 O (Z = 4) for this mineral, in contrast to Ca 5 (AsO 4 ) 2 (AsO 3 OH) 2 ·5H 2 O (Z = 3) documented in the literature. The chemical compositions for R100075 and R080001 are Ca 4.03 (AsO 4 ) 2 (As 0.99 O 3 OH)·4H 2 O and Ca 3.97 (AsO 4 ) 2 (As 1.01 O 3 OH)·4H 2 O, with trace Zn and Mn, respectively. The structure is characterized by undulating layers formed by the four nonequivalent, rather irregular Ca polyhedra [Ca1O 6 (H 2 O), Ca2O 6 (H 2 O), Ca3O 4 (H 2 O) 3 , and Ca4O 5 (H 2 O) 3 ] linked through the sharing of edges and vertices. These undulating layers are parallel to (010) and are interconnected by AsO 4 and AsO 3 OH tetrahedra, as well as hydrogen bonds, along the b axis. Vladimirite is remarkable inasmuch as one of the hydrogen-bonded O–H···O distances (O12H–H···O3) is only 2.465(2) A, which is the shortest donor–acceptor distance of all known Ca-bearing arsenate minerals, similar to the short donor–acceptor distances observed in several synthetic compounds containing AsO 3 OH groups.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 it