 Asbestos is an umbrella term that refers to six different naturally occurring silicate minerals composed of thin fibrous crystals. The fibers are made up of even smaller pieces called fibrils, which can be as small as a single micron in length. The most commonly used type is called chrysolite, or white asbestos, which makes up about 95% of the asbestos in most products, but a number of other kinds are recognized, including brown and blue asbestos.