Morphological and compositional data of erionite from Lessini Mounts, NE Italy

In the Lessini Mounts a volcanic activity developed from the late Paleocene to the late Oligocene (De Vecchi & Sedea, 1995) with the emplacement of submarine and subaereal lava flows and tuffs. These rocks (basanites, alkalibasalts, transitional basalts to tholeiites) are often deeply weathered, with vesicles and fractures filled by secondary minerals . These are mainly represented by zeolites such as phillipsite, harmotome, chabazite, analcime, gmelinite, natrolite, offretite and erionite. Recently, erionite has been carefully investigated because of its link to malignant mesothelioma (Dogan et al., 2006); Bertino et al., 2007). As a consequence, erionite has been classified as a Group I Human-Carcinogen by the International Agency for Research on Cancer and this makes it the most carcinogenic naturally occurring fibrous mineral known. In this work, we present morphological and compositional data on erionite crystals recently discovered in the Lessini Mts. (Mattioli et al., 2008). From a morphological point of view the studied samples show two different types of erionite. (1) Prismatic to acicular crystals ended by short hexagonal prisms of about 15 μm in diameter, whereas the main body of the crystals is extremely thin (diameter is 5 μm), is characterized by an excellent, prismatic cleavage and devoid of any geometry. (2) Fibrous crystals with diameter <1 μm and a length up to about 50 μm; these fibers are flexible and tend to intimately aggregate in parallel bundles of up to 10 μm in diameter. Erionite of both types show a great tendency to break down into fibers, which are potentially extremely pathogenic upon inhalation. In the type (1) the majority of the measured fibers is in the range 2-30 μm in length and 0.1-0.4 μm in diameter, whereas in the type (2) almost all of the measured fibres are 50 to 60 μm in length and <0.1 μm in diameter. The EDS spectra acquired on the bundles of fibers revealed the occurrence of Ca, Mg, Na, and K as extra-framework cations. In addition, a small amount of Fe was detected. Preliminary semi-quantitative analyses in the type (1) fibers pointed out that chemical composition differs depending on the analytical point, indicating a significant inhomogeneity of the sample.