Asbestos is a set of six naturally occurring silicate minerals, which all have in common their asbestiform habit: i.e., long (roughly 1:20 aspect ratio), thin fibrous crystals, with each visible fiber composed of millions of microscopic "fibrils" that can be released by abrasion and other processes. They are commonly known by their colors, as blue asbestos, brown asbestos, white asbestos, and green asbestos.Asbestos was being mined more than 4,000 years ago, but large-scale mining began at the end of the 19th century, when manufacturers and builders began using asbestos for its desirable physical properties. Some of those properties are sound absorption, average tensile strength, affordability, and resistance to fire, heat, and electricity. It was used in such applications as electrical insulation for hotplate wiring and in building insulation. When asbestos is used for its resistance to fire or heat, the fibers are often mixed with cement or woven into fabric or mats. These desirable properties led to asbestos being used very widely. Asbestos use continued to grow through most of the 20th century, until public recognition of the health hazards of asbestos dust led to its outlawing by courts and legislatures in mainstream construction and fireproofing in most countries.
Inhalation of asbestos fibers can cause serious and fatal illnesses including lung cancer, mesothelioma, and asbestosis (a type of pneumoconiosis). Concern of asbestos-related illness in modern times began with the 20th century and escalated during the 1920s and 1930s. By the 1980s and 1990s, asbestos trade and use were heavily restricted, phased out, or banned outright in an increasing number of countries.Despite the severity of asbestos-related diseases, the material has extremely widespread use in many areas. Continuing long-term use of asbestos after harmful health effects were known or suspected, and the slow emergence of symptoms decades after exposure ceased, made asbestos litigation the longest, most expensive mass tort in U.S. history though a much lesser legal issue in most other countries involved. Asbestos-related liability also remains an ongoing concern for many manufacturers, insurers and reinsurers.