Asbestos

What is Asbestos?

Asbestos is a blanket term that geologists apply to several types of silicate minerals that have the tensile strength and chemically inert qualities of stone, but are nonetheless made up of relatively soft and flexible fibers that can be woven like wool, cotton, jute or hemp. Although there are dozens of such minerals that might be considered "asbestiform," or asbestos-like, the U.S. federal government recognizes only six of these as "officially" being asbestos. These are:

  • Chrysotile (serpentine)
  • Crocidolite
  • Amosite
  • Tremolite
  • Actinolite
  • Anthophyllite

Of these six varieties, only the first three have had any extensive commercial use, although the other three - particularly tremolite - have been known to contaminate products such as vermiculite and talc.

Asbestiform minerals are the product of complex geological process that occurs close to the Earth's crust and are found in deposits of ultramafic rock ("mafic" referring to its chemical composition of magnesium and ferrous metal, or iron).

Over time, these minerals interact with sodium and dihydrogen oxide just beneath the Earth's surface, where temperatures are much cooler than they are farther down. This process produces a chemical instability resulting in the unique molecular structure that makes chrysotile fibrous.

Chrysotile asbestos is the only type of asbestos in the serpentine group. Chrysotile is made up of magnesium and oxides of silicon and hydrogen. Chrysotile was the most commonly-used variety of asbestos. Its fibers are soft and curly and the molecules are arranged in such a way that bonds between the layers cause them to roll up like a rug, resulting in the shape of the fiber. Chrysotile is also known as "white" asbestos because of its color and comprises 95 percent of the asbestos in use.

Crocidolite and amosite (along with tremolite) are classified as amphibole asbestos. Although fibrous and pliable like chrysotile, they result from different geologic processes and have significant iron content. Their molecular structure is more crystalline than chrysotile. As a result, such amphibole fibers are long and straight and much harder than the latter variety. In the case of crocidolite, the cross-section of the fiber forms a diamond-shape. These fibers are like microscopic, sharp-tipped, keen-edged knife blades and cause similar damage on a molecular level when inhaled into the lungs. It is considered the most toxic form of asbestos.

Amosite is called "brown" asbestos because of the iron molecules that impart this color, although it can also appear green or gray as well. Crocidolite is generally blue or blue-gray in color, and is therefore known as "blue" asbestos. These types of amphibole asbestos were mined primarily in southern Africa and Australia.

Commercial Uses

Asbestos was commonly used because the mineral possesses an innate resistance to heat and fire. This made it ideal for use in both industrial and domestic products (such as appliances). The fibers are extremely flexible and thin, but when spun into thread and woven into cloth, are virtually indestructible by sea water, chemicals and heat. The fibers are also mixed with products like cement to make them stronger and more flexible.

In the United Stated chrysotile asbestos was mined extensively at Libby, Montana by the W.R. Grace & Company, which used the mineral in dozens of building and insulation products. It is still an ingredient in Monokote, a type of spray-on insulation that was used extensively in building construction during the 1950s through the 1970s. The World Trade Center towers reportedly contained between two and five thousand tons of this material.

Most of the world's chrysotile today is produced in Russia, China and Canada. It continues to be used in firebrick, joint compound, adhesives, automotive brakes and other friction products as well as protective clothing used in chemical labs and around fire hazards.

"Blue" crocidolite was also used extensively in fire-proofing applications. Because it is an extremely poor conductor of electrical current, crocidolite asbestos was commonly found in and around electrical systems and power generation plants, where it was used as insulation. "Brown" amosite, like most types of rock, is chemically inert. While it shares the fireproof qualities of other varieties of asbestos, it was particularly suited to facilities in which caustic chemicals were used and produced, such as chemical labs and oil refineries.

Dangers of Asbestos

Asbestos is comprised of separate fibers. When the fibers are separated and airborne, they can be ingested or inhaled into the body, where they can become lodged in organs or body cavities. This can cause inflammation or infection overtime, which can eventually lead to the development of an asbestos-related disease such as mesothelioma, asbestosis or lung cancer. The fibers cause cellular damage in the body and the body has great difficulty ridding itself of the toxic fibers.

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