A general commercial term for two fibrous silicate-mineral groups: chrysotile, the fibrous serpentine mineral, and fibrous amphiboles (amosite, crocidolite, anthophyllite, tremolite, and actinolite) and these two groups are considered hazardous by U.S. regulatory agencies (e.g., Occupational Safety and Health Administration, OSHA). Asbestos minerals are incombustible, make excellent thermal and electrical insulators, resist chemical attack, and have high tensile strength. In addition to being fibrous, other characteristics include flexibility and the ability of fibers to be separated (often capable of being woven). The aspect ratio (i.e., length-to-width ratio) is often defined (as stated within Federal Register, June 8, 1992) as at least 20:1 (and often greater than 100:1) by mining or stone companies. Actinolite and tremolite have no commercial value. Amosite (“brown asbestos”) is a variety of grunerite (along the cummingtonite-grunerite join) whereas crocidolite (“blue asbestos”) is a variety of riebeckite. Asbestos minerals have been implicated as pathogenic when inhaled, although the minerals are not equally pathogenic with chrysotile, which is considerably less dangerous than the amphiboles. OSHA (Federal Register, June 8, 1992) considers asbestos fiber dimensions as the best indicator of significant “fiber pathology”. OSHA considers fiber-dimension lengths most pathologically active at greater than 5 micrometers and these fibers generally have aspect ratios of greater than 10:1 with most greater than 20:1.
Cf., aspect ratio, asbestiform, asbestosis