Types of Asbestos

The term "asbestos" refers to six fibrous minerals that have been commercially exploited and occur naturally in the environment. The U.S. Bureau of Mines has named more than 100 mineral fibers as "asbestos-like" fibers, yet only six are recognized regulated by the U.S. government. This is largely due to influential lobbying by the asbestos and stone industries, which powerfully shaped how the public perceives asbestiform minerals. The six asbestiform minerals recognized by the government include, tremolite asbestos, actinolite asbestos, anthophyllite asbestos, chrysotile asbestos, amosite asbestos, and crocidolite asbestos. Each of these minerals is categorized into two groups, serpentine and amphibole. Chrysotile asbestos is the only member of the serpentine group and the others belong to the amphibole group. The difference between these two groups is characterized by the physical components of the asbestos fibers. The serpentine group is made up of minerals that have a layered form and curly fibers and the latter group contains minerals that have straight fibers with a chain-like structure.

In order to fully understand the importance and function of these minerals, it is necessary to examine each mineral in more detail.

Chrysotile asbestos is better known as white asbestos and is made up of fine, silky, flexible white fibers. Chrysotile consists of minerals crystallized in a serpentine pattern, which means its crystals are formed in sheets. This is the most common type of asbestos comprising approximately 95 percent of all asbestos commercially used in the United States. Due to the widespread use of this fiber, chrysotile accounts for the majority of asbestos-related health problems throughout the world.

Tremolite is a relatively common mineral found in most metamorphic rocks. Its color ranges from a creamy white to dark green. Tremolite asbestos has been used for industrial purposes (though not as much as chrysotile) and has been identified as an ingredient in some household products, primarily talcum powder (which is also a known carcinogen). This form of asbestos is the major asbestiform contaminant of the infamous vermiculite mine in Libby, Montana.

Actinolite asbestos is a relatively common mineral existing in metamorphic rocks. This type of asbestos is usually green, white, or gray and it is closely related to the aforementioned tremolite mineral (actinolite contains a greater presence of iron over magnesium than tremolite). Actinolite does not have a strong history of commercial or industrial use, but it may be a contaminant in asbestos products. There are non-fibrous variants of actinolite that do not pose the same health threats associated with exposure to commercially exploited forms of asbestos.

Anthophyllite asbestos is commonly identified by its brittle white fibers that are made of crystals and have a chain-like appearance. This type of asbestos is formed by the breakdown of talc in ultramafic rock, and as such, anthophyllite is a common contaminant of talc. Although anthophyllite asbestos is not often used for industrial purposes, the fibers can occasionally be found among natural minerals that expand with the application of heat, such as vermiculite (which is commonly added to gardening soil).

Amosite asbestos is identified by its straight, brittle fibers that are light gray to brown in color. Amosite is also referred to as brown asbestos and its name is derived from the asbestos mines located in South Africa. In years past, amosite was often used as an insulating material and at one time it was the second-most commonly used type of asbestos. Throughout recent decades, commercial production of amosite has decreased and its use as an insulating material has been banned in many countries.

Crocidolite asbestos, better known as blue asbestos, is markedly identified by its straight blue fibers. This form is believed to be the most lethal form of asbestos. Crocidolite asbestos occurs naturally in locations such as Australia, South Africa, Bolivia, the former Soviet Union, and Canada.