According to the U.S. Bureau of Mines there are about 100 mineral fibers that are "asbestos-like" fibers but only six of them are recognized and regulated by the US government. When mentioning asbestos, most of the time these 6 fibrous minerals are being referred to.
The six asbestos minerals recognized by the government are:
- tremolite asbestos
- actinolite asbestos,
- anthophyllite asbestos,
- chrysotile asbestos,
- amosite asbestos,
- crocidolite asbestos.
These six types are broadly classified into two groups: 1}Serpentine group consisting only of the chrysolite asbestos , 2} Amphibole group consisting of the remaining five different asbestos.
The difference between these two main groups is in their physical structure, the serpentine group is made up of minerals that have a layered form and curly fibers while the amphibole group contains minerals that have straight fibers with a chain-like structure.
These are also known as white asbestos and they are made up of fine, silky, flexible white fibers. Chrysotile consists of minerals crystallized in a serpentine pattern that means it consists of crystals that are formed in sheets. It is the commonest type of asbestos accounting for 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.
This type of asbestos is found commonly 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 main asbestos type found in the infamous vermiculite mine in Libby, Montana.
This is a relatively common mineral also found in metamorphic rocks. The colour of this type of asbestos is usually green, white, or gray and it is closely related to the 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.
This type of asbestos fibers is commonly identified by its brittle white fibers that are made of crystals and have a chain-like appearance. This type of asbestos 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).
This type of asbestos is identified by its straight, brittle fibers that are light gray to brown in color. Amosite is also known as brown asbestos. 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.
These are commonly known as blue asbestos, and it is identified by its straight blue fibers. This form is believed to be the most dangerous form of asbestos. Crocidolite asbestos occurs naturally in locations such as Australia, South Africa, Bolivia, the former Soviet Union, and Canada.