Fluoro-edenite from Biancavilla (Catania, Sicily, Italy): crystal chemistry of a new amphibole end-member

Fluoro-edenite, ideally NaCa2Mg5(Si7Al)O22F2, was found both as prismatic or acicular crystals of millimetric size and as fibers in the rock cavities in gray-red altered benmoreitic lavas occurring at Biancavilla (Etnean Volcanic Complex, Catania, Italy). It is associated with feldspars, quartz, clino- and orthopyroxene, fluoro-apatite, ilmenite, and hematite, and probably crystallized from late-stage hydrothermal fluids. Fluoro-edenite has been characterised by electron microprobe analysis, X-ray structure refinement and IR spectroscopy. Structure refinement allowed determination of cation site-preference and ordering. The discovery and characterisation of the new amphibole end-member fluoro-edenite is important for two main reasons. The first reason involves mineral systematics and nomenclature, and fluoro-edenite enlarges the compositional fields of a rather rare and still not well known amphibole subgroup. More important, it allowed to understand that the amphibole compositions which can crystallise as fibers are more than previously thought. The second reason, perhaps the more important for interdisciplinary researches and for human health, is that the occurrence of fluoroedenite at Biancavilla (Mt.Etna, Sicily) could be related to the anomalously high incidence of mesothelioma, a rare deadly pathology which is caused by environmental pollution and especially to the presence of asbestos.