Multi-method characterization of Asbestiform Antigorite from South Australia
Bibliographic record
Abstract
Antigorite occurs in several locations worldwide and is defined as the simple serpentine Mg3Si205(OH)4 polymorph that compensates for the silica tetrahedral layer (Si2O5 sheet) misfit with the octahedral brucite Mg(OH)2 layer by regular structural undulation down the “b” crystalline axis. The chrysotile polymorph of the same chemistry compensates for the misfit in full rolls or scrolls along “b” axis, which can form fine fibres, and is the most common mineral in commercial asbestos. Chrysotile is therefore always asbestiform, but antigorite can exhibit a variety of crystalline habits in hand sample and the microscope, from massive, to platy, to bladed, and (occasionally) fibrous, but is not regulated as asbestos. Here, we performed a multi-method study in order to characterize a highly fibrous asbestiform occurrence of antigorite from Rowland Flat, South Australia. In comparison to HSE Canadian chrysotile, we show that optical (PLM) and transmission electron microscopy (TEM) allows to distinguish this antigorite from chrysotile. Based on PLM analysis with CS dispersion staining, chrysotile is magenta parallel (ǁ) to the polarizer and exhibits blue perpendicular (Ʇ) colours while this antigorite exhibits gold to golden magenta ǁ and blue-magenta Ʇ colours (1.550 HD RI at 25◦C). Also, we demonstrate SAED-TEM patterns for the two specimens to distinguish chrysotile “enrolled” crystal structure from the undulating antigorite structure, focusing on the highly characteristic [110] zone rel-rod streaking versus systematic repeats. Scanning electron microscopy (SEM) images were collected to further investigate the asbestiform nature of the antigorite from Rowland Flat. We show that the dominant morphology of Rowland Flat antigorite is of microscopic laths that split into very thin needles. In order to further investigate the morphometric parameters of this fibrous antigorite, individual fibres were measured at 20,000-25,000x by TEM. We show that the majority of these structures meet or exceed WHO fibres criteria, display high mean aspect ratios, ranging from 20:1 up to more than 100:1, and display widths lower than 1 µm, which in the literature is definition for asbestos fibres. Finally, our data indicate that the antigorite from Rowland Flat exhibits all characteristics of the asbestiform habit as defined in international standards (i.e., EPA/600/R-93/116), supporting the need for regulation of asbestiform antigorite as asbestos.
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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 | 0.001 |
| 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".