Quantitative classification of asbestos-like morphology for assessing potentially hazardous fibrous minerals

Hazard assessment of naturally occurring asbestos and asbestos-like minerals (NOA) is hindered by the lack of standardized criteria for quantifying asbestos-like morphology. This work introduces the fibrosity parameter (F_p), an experimental approach for classifying suspected fibrous minerals. F_p combines standardized mechanical stress with automated morphometric analysis to evaluate changes in the percentage of elongate mineral particles (EMP) during milling. The approach was tested on five antigorite and three tremolite samples spanning fibrous, lamellar, and prismatic morphologies, using crocidolite, amosite, MMVF, and talc as references. F_p is defined by EMP% after 20 min of milling (EMP₂₀%) and the slope of EMP% between 2 and 20 min (S). Thresholds of EMP₂₀% = 50% and S = -1 distinguished four morphological scenarios: 1) asbestos or asbestos-like, 2) precautionary asbestos-like, 3) non-asbestos-like, and 4) non-asbestos. Fibrous antigorite samples and one tremolite retained high EMP contents and behaved comparably to asbestos references, whereas another macroscopically fibrous tremolite progressively lost fibrosity and was classified as non asbestos-like. Thus, macroscopic fibrosity is not a reliable proxy for asbestos-like fragmentation behaviour. F_p provides a quantitative and reproducible morphological screening tool that complements broader hazard assessment. However, F_p is not a stand-alone predictor of pathogenicity.