Asbestos

Types of Asbestos

The term "asbestos" refers to a sizable group of silicate minerals - essentially different kinds of stone - that are characterized by a unique molecular structure allowing them to be woven like cotton, hemp or jute and made into fabric. It also has an extremely high tensile strength in relation to its weight, and like any other stone, it is resistant to flame as well as caustic and corrosive chemicals.

According to the U.S. Bureau of Mines, there are more than 100 mineral fibers that fall into the asbestiform category, but only six of these have been "officially" classified as asbestos and subject to any sort of regulation.

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

Of these six varieties, only those marked with the asterisk (*) have been commonly used in commercial and/or industrial applications. However, tremolite and other types of asbestos have been known contaminants in other products such as vermiculite and talc.

Chrysotile

This is by far the most common form of asbestos used commercially over the years. Also known as "white" asbestos, it was extensively mined by the W.R. Grace Corporation in Libby, Montana. Currently, the world's primary source of this substance is the mining operation in Thetford, Quebec. Canada continues to export thousands of tons of chrysotile asbestos every year, primarily to developing nations. Other large chrysotile producing countries include Russia and China.

Chrysotile is also called "serpentine" because of its curly appearance. These white fibers are relatively soft and pliable, which makes them useful in a wide range of products such as insulation, fire-proof clothing and fabric and gaskets. Chrysotile accounts for 95 percent of all the asbestos used commercially as well as the vast majority of asbestos disease cases. Although it has been implicated in asbestos cancer, non-malignant asbestosis is a far more common disease caused by this variety.

Amosite and Crocidolite

Also known as "blue" and "brown" asbestos, these are two types of asbestos that geologists classify as amphibole. These are considered to be the most deadly forms of asbestos, and the kind most strongly associated with mesothelioma and other forms of asbestos cancer.

Amosite - the name of which comes from "Asbestos Mines Of South Africa - is characterized by straight, brittle fibers that range in color from grayish-yellow to dark brown. Amosite was second only to chrysotile when it came to its use in commercial and industrial applications. Because of its iron content, amosite was particularly resistant to caustic chemicals and was used extensively in factories, laboratories and refineries where such chemicals were used. Interestingly, it was among South African asbestos miners that pleural mesothelioma was first identified as a form of cancer distinct from that of the lungs.

Crocidolite - the "blue" variety - also consists of straight, hard fibers that have been compared to microscopic spears or needles. It is generally considered to be the deadliest form of asbestos, and was mined and processed primarily in South Africa as well as Australia - a country with some of the highest rates of mesothelioma in the world. Crocidolite has primarily been valued for its resistance to electrical current, and is therefore used extensively in power generation plants and other electrical systems. Incredibly, crocidolite was even used in a commercial cigarette filter during the 1950s. Both of these amphibole types of asbestos were used extensively in ship construction.

Tremolite

Tremolite asbestos was not actually mined or marketed commercially to any large extent, but was a major contaminant in an insulation and gardening product marketed by W.R. Grace & Company, known as vermiculite and marketed under the proprietary brand-name of Zonolite. Because of this, tremolite poses a risk for those who work in old buildings as renovators and demolition workers.

Tremolite, which ranges in color from light gray to dark green, was present at the mining operation in Libby Montana. Also considered a type of amphibole asbestos, its fibers are rigid and highly toxic. Exposure to tremolite has been known to cause mesothelioma and other asbestos-related cancers.

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