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Asbestos (pronounced or ) is a set of six naturally occurring silicate minerals,〔 which all have in common their eponymous asbestiform habit: 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 mining existed 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 because of its desirable physical properties:〔 sound absorption, average tensile strength, its resistance to fire, heat, electrical and chemical damage, and affordability. 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 made asbestos a very widely used material, and its use continued to grow throughout most of the 20th century until the knowledge of carcinogenic effects of asbestos dust caused its effective demise as a mainstream construction and fireproofing material in most countries. It is now known that prolonged inhalation of asbestos fibers can cause serious and fatal illnesses including lung cancer, mesothelioma, and asbestosis (a type of pneumoconiosis).〔(Position Statement on Asbestos from the Joint Policy Committee of the Societies of Epidemiology (JPC-SE) ), approved June 4, 2012〕 Health issues related to asbestos exposure can be found in records dating back to Roman times. By the beginning of the 20th century concerns were beginning to be raised, which escalated in severity during the 1920s and 1930s. By the 1980s and 1990s asbestos trade and use started to become banned outright, phased out, or heavily restricted in an increasing number of countries. The severity of asbestos-related diseases, the material's extremely widespread use in many areas of life, its continuing long-term use after harmful health effects were known or suspected, and fact that asbestos-related diseases can emerge decades after exposure ceases, have resulted in asbestos litigation becoming the longest, most expensive mass tort in U.S. history and a much lesser legal issue in most other countries involved. Asbestos-related liability also remains an ongoing concern for many manufacturers, insurers and reinsurers. ==Types and associated fibers== Six mineral types are defined by the United States Environmental Protection Agency as "asbestos" including those belonging to the serpentine class and those belonging to the amphibole class. All six asbestos mineral types are known to be human carcinogens.〔(【引用サイトリンク】title=Asbestos, CAS No. 1332-21-4 )〕 The visible fibers are themselves each composed of millions of microscopic "fibrils" that can be released by abrasion and other processes.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Asbestos」の詳細全文を読む スポンサード リンク
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