Asbestos (pronounced: /æsˈbɛstɒs/ or /æsˈbɛstəs/) is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into the atmosphere by abrasion and other processes. Inhalation of asbestos fibres can lead to various serious lung conditions, including mesothelioma, asbestosis, and lung cancer, so it is now notorious as a health and safety hazard.[1]

Fibrous tremolite asbestos on muscovite
CategorySilicate minerals
Strunz classification09.ED.15
Dana classification71.01.02d.03
Crystal systemOrthorhombic, monoclinic
Formula mass277.11 g
ColorGreen, red, yellow, white, gray, blue
Crystal habitAmorphous, granular, massive
Mohs scale hardness2.5–6.0
Specific gravity2.4–3.3
Optical propertiesBiaxial
Refractive index1.53–1.72
2V angle20° to 60°
DispersionRelatively weak
ExtinctionParallel or oblique
Ultraviolet fluorescenceNon-fluorescent
Melting point400 to 1,040 °C (752 to 1,904 °F)

Archaeological studies have found evidence of asbestos being used as far back as the Stone Age to strengthen ceramic pots,[2] but large-scale mining began at the end of the 19th century when manufacturers and builders began using asbestos for its desirable physical properties. Asbestos is an excellent electrical insulator and is highly heat-resistant, so for much of the 20th century it was widely used across the world as a building material until its effects on human health were recognized in the 1970s.[3][4] Many modern buildings constructed before the 1980s are thought to contain asbestos.[5]

The use of asbestos for construction and fireproofing has been made illegal in many countries.[1] Despite this, at least 100,000 people are thought to die each year from diseases related to asbestos exposure. In part, this is because many older buildings still contain asbestos; in addition, the consequences of exposure can take decades to arise.[5][6]

Many developing countries still support the use of asbestos as a building material, and mining of asbestos is ongoing, with top producer Russia having an estimated production of 790,000 tonnes in 2020.[7]