A mineral with a fine fibrous structure based on silicate compounds. The three most important types are chrysotile asbestos (white), crocidolite asbestos (blue) and amosite asbestos (greyish brown). Chrysotile asbestos fibres can be spun but are sensitive to acid. Crocidolite asbestos fibres are more resistant and harder. Asbestos combines a number of physical and chemical properties: incombustibility, heat resistance, chemical resistance, rot and corrosion resistance, low electrical conductivity, high elasticity and tensile strength, and special capabilities of adsorption of thermal insulation. Extensive health precautions and new advanced plastics have reduced the role played by asbestos in modern sealing systems to an insignificant one.