Windmountainite, □Fe3+2Mg2□2Si8O20(OH)2(H2O)4·4H2O, a new modulated, layered Fe3+-Mg-silicate-hydrate from Wind Mountain, New Mexico: Characterization and origin, with comments on the classification of palygorskite-group minerals
Bibliographic record
Abstract
ABSTRACT Windmountainite, ideally □Fe3+2Mg2□2Si8O20(OH)2(H2O)4·4H2O, is a new mineral species and member of the palygorskite group discovered as orange-brown, radiating aggregates that commonly fill vesicles (average 1.5 × 2.5 mm) within a phonolite dike at Wind Mountain, Otero County, New Mexico, USA. The mineral develops as tightly bound bundles (up to 0.02 × 6 mm) of acicular to bladed crystals that are elongate on [001] and flattened on the pinacoid {010}. Associated minerals include albite, aegirine, fluorapophyllite-(K), natrolite, neotocite, and montmorillonite, the last of these being observed to replace primary windmountainite. It has a dull luster, silky in aggregates, is translucent and has an orange-brown streak. It does not fluoresce under short-, medium-, or long-wave ultraviolet radiation. Windmountainite is brittle with a splintery fracture and has two good cleavages (predicted) on {110}, an estimated hardness of 2, a calculated density of 2.51 g/cm3, and a calculated navg of 1.593. A total of n = 30 EMPA (WDS) analyses from six grains yielded an average of (wt.%): Na2O 0.08, MgO 3.47, Al2O3 1.15, SiO2 49.76, Cl 0.07, K2O 0.40, CaO 0.68, TiO2 0.30, MnO 5.64, Fe2O3 20.17, H2O (calc.) 16.59, O=Cl –0.02, total 98.29. The empirical formula [based on Σ(T1, T2, M2, M3) = 12 cations pfu, excluding Ca, K, and Na] is: (□0.78Ca0.12K0.08Na0.02)Σ1.00(Fe3+1.93Al0.04Ti0.02)Σ1.99 (Mg0.81Mn2+0.75Fe3+0.44)Σ2.00□2(Si7.81Al0.17Ti0.01Fe3+0.01)Σ8.00O20[(OH)1.98Cl0.02]Σ2.00[(H2O)3.38(OH)0.62]Σ4.00·4H2O, yielding the simplified formula, □Fe3+2Mg2□2Si8O20(OH)2(H2O)4·4H2O. The predominance of Fe3+ is based on color, results from the crystal-structure refinement, the crystal-chemistry of palygorskite-group minerals, the association with Fe3+-dominant minerals, and considerations regarding the late-stage geochemical evolution of agpaitic rocks. The presence of H2O and OH was determined based on results from the refined crystal structure and Fourier-transform infrared spectroscopy. Windmountainite crystallizes in the space group C2/m with a 13.759(3), b 17.911(4), c 5.274(1) Å, β 106.44(3)°, V 1246.6(1) Å3, and Z = 2. The seven strongest powder X-ray diffraction lines are [d in Å (I), (hkl)]: 10.592 (100) (110), 5.453 (16) (130), 4.484 (19) (040), 4.173 (28) , 3.319 (53) (221, 400), 2.652 (30) , 2.530 (27) . The crystal structure was determined from single-crystal X-ray diffraction data and refined to R = 4.01% and wR2 = 10.70% using data from 902 reflections (Fo > 4σFo). It is based on sheets of inverted double chains of SiO4 tetrahedra that sandwich ribbons of Mφ6 octahedra (φ = O, OH, H2O, Cl), giving rise to large channels (∼6.5 × 9 Å) that are occupied by loosely held H2O groups. A modified classification of the palygorskite group [general crystal-chemical formula M1M22M32M42T14T24O20(OH)2(H2O,OH)4·W] is proposed based on the occupants of the four M sites. Within this scheme, windmountainite is the □-Fe3+-Mg-□ member. The palygorskite group includes six members: palygorskite (monoclinic and orthorhombic polytypes), yofortierite, tuperssuatsiaite, raite, windhoekite, and windmountainite. Windmountainite is considered to have formed from late-stage fluids that were alkaline, oxidized, and rich in both Fe3+ and H2O; high aH2O conditions are reflective of abundant, hydrated feldspathoids (natrolite and analcime) forming as primary rock-forming minerals in the phonolite at Wind Mountain.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.000 |
| 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) | 0.001 | 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 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".