Asbestos is the name of a group of minerals that occur naturally as masses of strong, flexible fibers that can be separated into thin threads and woven. It is a fibrous, silicate mineral known for its durability, heat-resistance, and chemical inertness. Asbestos has been widely used in many industrial products, including cement, brake linings, roof shingles, flooring products, textiles, and in a variety of building construction materials for insulation and as a fire-retardant.
These naturally occurring fibers have been mined and used for about the last 100 years with peak use in the 1970's. At that time adverse health effects were widely associated with the use of asbestos. Although asbestos use has drastically declined in the United States, it continues to be used in developing countries. There are three main types of asbestos.

Chrysotile (white asbestos) is the most common form of asbestos in the United States and Canada and may be the least harmful.

The fibers are fine, smooth, and white.
Amosite (brown asbestos) is most often used in thermal insulation systems. The fibers are brittle and straight.

Crocidolite (blue asbestos) consists of straight fibers and is used less often than the other two.

Products and buildings that include asbestos are known as Asbestos Containing Materials (ACM). Anthopylite, Tremolite, and Actinolite are three other forms of asbestos that can also be found in ACM.
The Environmental Protection Agency (EPA) and the Consumer Product Safety Commission (CPSC) have banned several asbestos products. Manufacturers have also voluntarily limited uses of asbestos. Today, asbestos is most commonly found in older homes, in pipe and furnace insulation materials, asbestos shingles, millboard, textured paints and other coating materials, and floor tiles. More information about asbestos can be found at http://www.epa.gov/iaq/asbestos.html and http://www.epa.gov/asbestos/.