Omongwaite, Na<sub>2</sub>Ca<sub>5</sub>(SO<sub>4</sub>)<sub>6</sub>.3H<sub>2</sub>O, a new mineral from recent salt lake deposits, Namibia
Bibliographic record
Abstract
Abstract Omongwaite, Na2Ca5(SO4)6.3H2O, is a new mineral, found as inclusions in gypsum crystals in recent salt lake deposits at Omongwa pan, Namibia. It is monoclinic, with space group C2, a = 12.08(3) A, b = 6.96(1) Å, c = 6.39(2) Å, B = 90.2(3)°, V= 537(2) Å3, and Z = 1. The six strongest lines in the X-ray powder diffraction pattern [dobs. (Å), (I/I° meas), (hkl)] are: 6.028, (40), (110); 3.484, (29), (310); 3.019, (51), (400); 3.014, (100), (220); 2.824, (34), (1̄12); and 2.820, (65), (112). Electron microprobe analysis, recalculated on the basis of 3H2O per formula unit (p.f.u.), gave 56.16 wt.% SO3, 30.82 wt.% CaO, 5.25 wt.% Na2O, 3.21 wt.% K2O, 6.25 wt.% H2O, totalling 101.69 wt.%. The empirical formula, based on 24 anhydrous oxygens p.f.u., is (Na1.47K0.59)Σ;=2.06Ca4.76S6.07O24.3H2O, yielding Na2Ca5(-SO4)6.3H2O as the end-member formula. Na/K ratios are variable, with an average of ∼2.5. The crystals are elongated, with pseudohexagonal transversal cross-sections and with sphenoidal terminations that are commonly developed at one end. The crystal structure of omongwaite is similar to that of bassanite, CaSO4.0.5H2O. Published studies of the synthetic phase show that it can be described as a bassanite structure in which one out of six Ca2+ ions are replaced by Na+ and a second Na+ ion occupies a position near those sites. The crystals are parallel to the [001] axis of the gypsum crystals in which they occur as inclusions. The mineral formed by topotactic replacement during interaction of gypsum with concentrated solutions. It is preserved where the affected surface became covered by gypsum by rapid growth shortly after the formation of omongwaite. The mineral is named after the locality where it was found.
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 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 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".