Fibrous ferrierite from Lovelock, Nevada, USA

Ferrierite is the name of a family of zeolite minerals that includes three species with the same topological framework (FER) but with different content of extra-framework cations. In Nevada (USA), the zeolite-rich tuff deposit of Lovelock is the largest occurrence of diagenetic ferrierite-Mg, one of the member of the family. Recent studies have shown that Lovelock ferrierite can exhibit fibrous-asbestiform crystal habit and may possess the same physical-chemical and crystallographic properties of carcinogenic fibrous erionite, Nevertheless, it has not yet been classified by the International Agency for Research on Cancer (IARC). Nowadays, outcrops hosting fibrous ferrierite are being mined in Nevada for commercial purposes. Dust generated by these excavation activities may expose workforces and general public to this potential natural hazard. The main goal of this study was to perform a mineralogical and morphometric characterisation of the tuff deposit at Lovelock and evaluate the distribution of fibrous ferrierite in the outcrop. For this purpose, a multi-analytical approach including X-ray powder diffraction, scanning and transmission electron microscopy techniques, micro-Raman spectroscopy, thermal analyses, and surface-area determination was applied. The results indicate that fibrous ferrierite is widespread in the deposit and intermixed with mordenite and feldspar, although there are variations in the spatial distribution in the bedrock. The crystal habit of the ferrierite ranges from prismatic to asbestiform (elongated, thin and slightly flexible) and fibres are aggregated in bundles. According to the WHO counting criteria, most of the ferrierite fibres can be classified as breathable. While waiting for confirmatory in vitro and in vivo tests to assess the actual toxicity/pathogenicity potential of this mineral fibre, it is recommended to adopt a precautionary approach for mining operations in this area to reduce the risk of exposure.