"Asbestos" is a generic name for a variety of fibrous minerals, meaning minerals that look like clusters of fine threads. Asbestos fibers are strong and nonflammable, so they have been used in a variety of products like firefighting suits, building and pipe insulation, ceiling plaster, floor tiles, theater curtains, and brake pads.

Three distinct minerals comprise most asbestos products—chrysotile, amosite, and crocidolite, known as white, brown, and blue, respectively. White (chrysotile) asbestos is the most commonly used variety, occurring in about 95% of asbestos products. It is a member of the large class of minerals collectively known as serpentine. Serpentine deposits are found in remnants of oceanic lithosphere that were shoved up onto the edge of continents during mountain building, such as occurs during collisions.

Environmental concerns about asbestos came to the attention of the public after some highly publicized lawsuits claiming that exposure to asbestos fibers caused mesothelioma, a rare form of cancer that attacks the lining of the chest and abdomen, and asbestosis, a disease in which the lungs become clogged with asbestos fibers, harden, and stop functioning.

Doctors think that asbestosis develops because some asbestos minerals break into 5-to-50-micron-long (1 micron = 10^-8 cm) fibers and are inhaled along with other dust; but unlike other dust, these fibers fit snugly into pores in the lung and stay put. The exact process by which asbestos causes cancer isn’t really known. According to one hypothesis, fibers may enter the bloodstream by piercing the lung and entering capillaries. Perhaps the fibers enter cells and somehow interfere with DNA, causing the cells to become malignant.

No one is certain whether all asbestos fibers are dangerous, or if only certain dimensions or compositions of the fibers are. Some studies suggest that white asbestos is less dangerous than brown or blue because its fibers are curly and cannot pierce the lung tissue. In any case, asbestos is most dangerous when it occurs as dust in the air, such as may happen in asbestos factories or mines, or when an asbestos-containing building is renovated. Asbestos that is sealed behind paint, tape, or drywall might not be much of a hazard. In many cases, the dust created by ripping asbestos out of a building may present more of a risk than the intact asbestos.

Because of the possibility that not all asbestos poses an extreme danger, some experts think that the immense effort to remove asbestos from buildings in the United States has actually increased the risk to occupants, because such work may cause asbestos to enter the ventilation system. Current regulations do not rigorously distinguish between the more dangerous and less dangerous types. Some geologists argue that it may be worthwhile to study the issue further before going ahead with universal removal of asbestos.

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