The Geology of Asbestos, Part II

Yesterday, we discussed the particular molecular bonds that create asbestos fibers, which allow them to have the tensile strength of stone and the flexibility of cloth. Chrysotile–the curly asbestos fibers that result from an uneven distribution of ions–are found in a type of rock known as serpentine. Serpentine is a type of metamorphic rock that form when igneous rocks low in silica and potassium, yet high in ferrous oxide (a compound of iron and water molecules) are exposed to high temperatures in the presence of water and carbon dioxide. Extreme heat and pressure cause the chemical structure of the igneous rock to change; the presence of carbon dioxide causes the ions (positively or negatively charged molecules) to form a flexible, fibrous structure. Serpentine may also contain trace amounts of chromium, manganese, cobalt and nickel. Amphibole rocks are composed of molecular chains that consist of one atom of silicon and four atoms of oxygen, linked to ions of iron and/or magnesium. They can also be of metamorphic origin; in this case, the transformation is caused by contact with carbon dioxide.

However, there are also amphiboles that are igneous in origin, and are found as constituents of granite or other types of igneous (heat-formed) rock. Tremolite, which was mined in Libby, Montana, as well as crocidolite and amosite, are examples of asbestos originating from igneous rock. In simplest terms, asbestos is what results when hot water reacts with rock that contains relatively low amounts of silicon, but high amounts of magnesium. The irony is that a substance with such deadly consequences for human health is the result of the interaction of two substances that are absolutely necessary for the maintenance of life. The need of living things for liquid water is well understood by most people. However, magnesium is also necessary for healthy cell function, and is the 11th most common element found in the human body. One dangerous misconception is the idea that chrysotile is somehow a “safe” form of asbestos because it is curly and softer than the amphibole type. It should be understood that most of the asbestos produced and used in the world is chrysotile–including that mined in Libby, Montana, where the rate of asbestos disease is 60 times the national average. <!–[if !supportEmptyParas]–> <!–[endif]–>