What is asbestos?

Asbestos is a group of naturally occurring fibrous silicates that is found in bundles of fibers in various rock types throughout the world. It occurs as two distinct types: serpentine asbestos with are curved, flexible fibers, and amphiboles, which are straight, thin and needle-like. It has been used for centuries, because of its heat resistance, durability and fibrous structure. The name asbestos is of Greek origin, and means 'unextinguishable' -- relating to its historical use in lamp wicks.

Chrysotile (white asbestos) is the only serpentine form. It is the form most commonly used commercially, and is thought to have the lowest association with malignant mesothelioma, because its larger, springy fibers are more likely to be cleared from the lungs after inhalation. However, chrysotile is associated with the development of other asbestos-related conditions, such as asbestosis. (Some experts believe it is not associated with mesothelioma at all, but that this cancer develops in those exposed to chrysotile because it is commonly contaminated with amphiboles.)

Amphiboles -- with their thin, needle-like fibers that are able to penetrate deep into lung tissue -- are the forms of asbestos that are associated with a high risk for developing malignant mesothelioma. There are five main types of amphiboles:

• crocidolite (blue asbestos)
• amosite (brown asbestos)
• anthophyllite (gray asbestos)
• tremolite
• actinolite.

Crocidolite and amosite are the amphiboles with the greatest risk of causing asbestos-related diseases and tremolite is that with the least risk.