# Asbestos: Communicating the Health Issues Derived from Fibrous Minerals to Society
## 3 Asbestos and Asbestosis  
### The Minerals  
The National Institute for Occupational Safety and Health (NIOSH) defines asbestos as any elongated particle, including fibrous minerals such as serpentine (mainly chrysotile) and fibrous amphibes (e.g., actinolite and tremolite) [23]. In the European Union, asbestos is defined as fibers with a length of more than five micrometers, a width of less than three micrometers, and a length/width ratio greater than 3:1 (Directive 2003/18/EU) [24]. All the mentioned minerals are chemically inert and heat-resistant, which led to the past use of asbestos for a wide variety of important industrial applications. However, these minerals are notably different. Amphiboles normally appear as prismatic phases, whereas serpentine (mainly chrysotile) appears as fibers (Figure 1a,b).  
Figure 1: Microscopic view of a serpentinized ultramafic rock from Cabo Ortegal (Galicia, Spain), where the original minerals are being transformed into serpentine and carbonate. The rigid amphibes can be distinguished from the flexible fibers of serpentine: (**a**) cross Nichols; (**b**) parallel Nichols.  
Asbestos is a fibrous mineral commonly found in metamorphic ultramafic rocks and is most frequently hosted by serpentinites. Serpentinites form through the metamorphism of ultramafic igneous rocks, involving fluids of different origins (Ref. [25] and the references therein). These rocks are characterized by a very low silica content and high quantities of Fe and Mg minerals (e.g., olivine and pyroxene), giving the rock a dark color. The original minerals in igneous rocks, mainly olivine and pyroxene, transform into amphiboles and serpentine (antigorite, lizardite, and chrysotile) during metamorphism, which is highly influenced by the temperature and composition of the transforming fluids.  
In some countries, \"amianthus\" is used to refer to asbestos, although this term is used more in industrial contexts. Additionally, amianthus is a silky variety of asbestos that can be knitted to produce textiles that have the useful thermal properties of asbestos [26]. However, \"asbestos\" refers to a whole mineral family, all of which are fibrous minerals, and the differences in the shapes of the minerals in this family should be clarified when explaining the societal problems derived from asbestos. Scientific experts should communicate these differences, as they are able to reply to any questions that arise.  
The problems that arise from the use and manipulation of these minerals are owing to the lack of knowledge of their nature. The danger is not only related to the shape of the mineral [27] but also to the chemical composition, as the real formula (e.g., for serpentine, Mg\({}_{3}\)[Si\({}_{2}\)O\({}_{5}\)](OH)\({}_{4}\)) often deviates from the theoretical formula, so these minerals may include potentially toxic elements, including various minor and trace elements (heavy metals, e.g., Cr, Mn, Co, Ni, Cu, Zn, Be, Ad, Rb, Sb, Ba, Pb, and Sr) [3]. Asbestos can be a main phase in rocks and be released when disturbed, (e.g., quarry extraction, the production of construction materials, and the restoration of monuments through laser cleaning [28]). Asbestos was frequently used in different industry sectors from the 19 th to most of the 20 th century (Table 1).