Wilcoxite MgAl(SO4)2F*17H2O, from Rico, Colorado: Occurrence and crystal structure
Bibliographic record
Abstract
Wilcoxite, (Mg 0.81 Mn 0.07 Fe 0.04 Zn 0.04 )∑ 0.96 Al 1.01 (SO 4 ) 2 F 1.02 •17H 2 O, is a secondary sulfate mineral that occurs in hydrothermal systems containing significant amounts of fluorine. A sample of wilcoxite was collected from abandoned mine workings east of Rico, Dolores Co., Colorado, U.S.A., where it occurs as white, efflorescent crusts composed of small anhedral crystals within a timber crib that protected the material from direct exposure to rain and snow, but not from changes in the humidity and temperature of the atmosphere. It is remarkable that this highly hydrated mineral has remained stable under these conditions. Unit cell dimensions are a 6.644(1), b 6.749(2), and c 14.892(3) A, α 79.664(4)°, β 80.113(4)°, γ 62487(3)°, and V 579.6(2) A 3 , space group P The previously unknown crystal structure was determined from single-crystal X-ray diffraction data and consists of isolated sulfate tetrahedra, Mg(H 2 O) 6 octahedra, and Al(H 2 O,F) 6 octahedra connected only through hydrogen bonding involving additional water molecules. Wilcoxite has 1.5 water molecules per sulfate tetrahedron that do not participate in the formation of an Al(H 2 O,F) 6 or Mg(H 2 O) 6 octahedron. The water molecules held within the epsomite (MgSO 4 •7H 2 O) structure are lost if the relative humidity (RH) drops below 50% at 298 K, and hexahydrite (MgSO 4 •6H 2 O) loses water to form starkeyite (MgSO 4 •4H 2 O) at 40% RH at 298 K. The fact that wilcoxite, with such a high water content, is stable when the magnesium sulfate with which it coexists has become starkeyite indicates that water molecules are more tightly bonded within the wilcoxite structure. If epsomite crystals are warmed slightly they slowly become first translucent and then an opaque white powder, whereas wilcoxite does not dehydrate but abruptly melts when warmed. This behavior is similar to the incongruent melting of meridianiite (MgSO 4 •11H 2 O) on warming above 2 °C.
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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 | 0.001 |
| 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) | 0.001 | 0.001 |
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".