The Mineralogy, Geology and Main Occurrences of Chrysotile

Chrysotile has been described as a “wonder” mineral because of its long, ultrathin, durable, flexible, and sometimes woven fibers. This peculiar crystal morphology, together with its chemical composition and crystal structure, determine unique thermal, electrical, and mechanical properties that have enabled chrysotile to be used in a number of industrial products or applications, from plastics to cement, from friction materials to vinyl tiles, and so on (e.g., Ross, 1981; Virta and Mann, 1994; Ross and Virta, 2001). Chrysotile fibers are classified, for commercial use, into fiber length groups, each one with its own subgroups (grade), with the longest fibers assigned to Group 0 and the shortest to Group 7. Each group has a specific use, the longer has been used in textiles, the shorter as a filler in various materials (cement, plastic, vinyl, etc.) The use of chrysotile for manufacturing industrial products began in the early decades of the twentieth century and its story is reflected in the worldwide consumption of asbestos that has increased from about 175 kilotonne (in the 1920) up to 4.8 megatonne (in the 1980) (Virta, 2006). Production of chrysotile asbestos in 2012 was around 2 kilotonne a year with the main producers being Russia (50%), China (22%), Brazil (15%), Kazakhstan (12%), (U.S. Geological Survey, 2013). USA and Canada were once among the main producers but now the mineral extraction is banned there, as well as in many European countries, because all forms of asbestos have been judged to be carcinogenic by the World Health Organization (WHO, 1988) and International Agency for Research on Cancer (IARC, 1977, 1987). However, it is widely recognized that chrysotile is less dangerous than amphiboles and that its low inhalation does not represent a risk for health although a prolonged exposure can produce health diseases (e.g., Sporn and Roggli, 2004; Bernstein et al., 2013 and references therein). Experimental evidence shows that chrysotile can be degraded by acid fluids such as those present in the lung (e.g., Rozalen et al., 2014). This implies that the genotoxic and carcinogenic potentials of this serpentine mineral are surely enhanced by the presence of amphiboles, and more frequently tremolite asbestos. Chrysotile free from other potentially dangerous minerals, or its analogous synthetic material, may be looked at with interest for new applications as nanotubes. Chrysotile, as well as the other two minerals forming the serpentine group-antigorite and lizardite-, is the principal mineralogical components of serpentinites, fine grained ultramafic rocks that are exposed in almost all continents, including Antarctica. These hydrous magnesium silicate phases generally form through hydrothermal alteration of ultrabasic rock-forming minerals, such as olivine and ortho/ clinopyroxenes. The reaction that leads to the formation of chrysotile, antigorite, and lizardite may be conventionally described as follows:

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