INSIGHTS INTO ASTROPHYLLITE-GROUP MINERALS. II. CRYSTAL CHEMISTRY
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Bibliographic record
Abstract
The crystal chemistry of 20 specimens of astrophyllite-group minerals from seven localities has been studied using a combination of single-crystal X-ray analysis of the structure and electron-microprobe analyses. Members of the astrophyllite group are triclinic ( P 1) and monoclinic ( C2/c or A 2) heterophyllosilicates with the general formula A 2 BC 7 D 2 T 8O26(OH)4 X 0–1, where A = [10]–[13]K, Rb, Cs, Na, H3O+, H2O, or □; B = [10]Na or Ca; C = [6]Mn, Fe2+, Fe3+, Na, Mg, or Zn; D = [6]Ti, Nb, or Zr; T = Si and Al, and X = F, OH, O, or □. The structure consists of two composite sheets, a heterogeneous ( H ) sheet and a sheet of octahedra ( O ), stacked along [001] in a 2:1 ratio. These 2:1 composite layers are bonded via a shared apical D ϕ6 anion through an interlayer containing an ordered array of K and Na, resulting in a layered HOH structure reminiscent of the TOT structure in 2:1 phyllosilicates. There are four crystallographically distinct M O6 octahedra in the O sheet; they host Mn, Fe2+, Fe3+, Na, Mg and Zn. The M (1) octahedron, the largest and least distorted within the O sheet, is host predominantly to Mn and Fe2+, with significant Na (up to 0.274 apfu ). The M (2) octahedron is highly distorted and contains predominantly Mn and Fe2+, whereas the M (3) and M (4) octahedra are the smallest and are occupied by Mn, Fe2+, Fe3+, Mg and Zn. The H sheet consists of open-branched zweier [100] single [Si4O12]8− chains cross-linked by corner-sharing D ϕ6 octahedra in triclinic species and kupletskite- Ma 2 b 2 c , and D O5 polyhedra in magnesium astrophyllite. Distortion of the D ϕ6 octahedron is minimized by (Nb,Zr) ⇔ Ti substitution, resulting in displacement of the cation toward the center of the octahedron. The composition of the [Si4O12]8− chains does not vary; there is essentially no Al, and Mossbauer spectroscopy did not indicate the presence of [4]Fe3+. Lateral fit of the O and H sheets is accomplished primarily by: (1) flattening of O -sheet octahedra, (2) tilting of the H -sheet tetrahedra out of the (001) plane, and (3) elongation or thickening of the tetrahedra along [001].
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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 it