GEORGEROBINSONITE, Pb4(CrO4)2(OH)2FCl, A NEW CHROMATE MINERAL FROM THE MAMMOTH - ST. ANTHONY MINE, TIGER, PINAL COUNTY, ARIZONA: DESCRIPTION AND CRYSTAL STRUCTURE
Bibliographic record
Abstract
Georgerobinsonite, Pb 4 (CrO 4 ) 2 (OH) 2 FCl, is a new chromate mineral species from the Mammoth – St. Anthony mine, Tiger, Pinal County, Arizona. It occurs as minute intergrowths of thin tabular orange crystals less than 0.1 mm across with {001} dominant and minor {010} and {110}, associated with caledonite, a cerchiaraite-related mineral, cerussite, diaboleite, Cr-bearing leadhillite, matlockite, murdochite, pinalite, wulfenite and yedlinite, in vugs in a silicified matrix. Georgerobinsonite is orange-red, transparent and has a pale orange streak and an adamantine luster, and it does not fluoresce under ultraviolet light. No cleavage or parting was observed. The Mohs hardness is 2½–3; georgerobinsonite is brittle with an uneven fracture. The calculated density is 6.23 g/cm 3 . The indices of refraction are α ≈ 2.07, β > 2.11, γ > 2.11; 2 V (obs) = 84(2)°; it is strongly pleochroic, α orange, γ yellow; optical orientation: X = a , Y = c and Z = b , and the dispersion is strong with r > v . Georgerobinsonite is orthorhombic, space group Pmmn , a 7.613(2), b 11.574(3), c 6.883(2) A, V 606.5(3) A 3 , Z = 2, a:b:c = 0.6578:1:0.5947. The strongest six lines in the X-ray powder-diffraction pattern [ d in A( I )( hkl )] are: 2.131(100)(232), 3.308(80)(012), 3.195(80)(211, 220), 6.371(60) (110), 3.357(60)(031, 201) and 3.143(60)(102). Chemical analysis with an electron microprobe gave CrO 3 14.79, PbO 77.99, SO 3 1.64, F 1.47, Cl 3.39, H 2 O (calc.) 1.52, sum 99.42 wt.%; the valence states of Pb, Cr and S, and the amount of H 2 O, were determined by crystal-structure analysis. The resulting empirical formula, on the basis of 12 (O, F, Cl, OH) anions, is Pb 4.09 (Cr 6+ 1.73 S 6+ 0.24 ) ∑1.97 O 8 (OH) 1.98 F 0.90 Cl 1.12 . The crystal structure of georgerobinsonite was solved by direct methods and refined to an R 1 index of 2.0% based on 574 observed reflections collected on a four-circle diffractometer with Mo K α X-radiation. There are two Pb 2+ cations coordinated by eight and nine anions, and both show prominent lone-pair stereoactive behavior. The Pb polyhedra share faces and edges to form layers parallel to {001} that are linked into a heteropolyhedral framework by (CrO 4 ) groups, with hydrogen bonding between OH and Cl anions. The mineral is named after Dr. George Willard Robinson (b. 1946), mineral curator, researcher, teacher and field collector.
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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 | 0.002 | 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) | 0.003 | 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".