CASITILE, THE NEW ASBESTOS (Revised) Page 2: The Sources of Misunderstanding
THE SOURCES OF MISUNDERSTANDING
‘Asbestos’ is not a mineral in itself. It is a collective term given to a group of minerals whose crystals occur in fibrous forms. The term ‘asbestos’ was adopted for the purposes of commercial identification alone; any use of the word to define the properties of the minerals within the group as if they were all the same is a serious scientific error.
The major minerals covered under the umbrella term ‘asbestos’ are listed in Table 1.
Table 1. Minerals covered by the term ‘asbestos’
Name |
Formula |
Chrysotile |
Mg3 Si4 O10 (OH)2 |
These 6 minerals, are members of two quite distinct mineralogical groups. Chrysotile is a serpentine mineral, the other 5 are all amphibole minerals. The name ‘chrysotile’, derives from the Greek for ‘fine golden hair’ (chrysos - "gold" and tilos - "fiber) (Browne, 2003). This mineral has long, flexible silky fibres unlike the straight rigid fibres of the amphiboles. The magnesium oxide/hydroxide surface of chrysotile (brucite) means it is chemically unstable in an acid milieu. It can be degraded by even a weakly acid environment such as that found in the lungs. Animal experiments have shown that chrysotile has low biopersistence with half-lives from a few hours to 15 days depending on the minerals origins. (Bernstein DM, Rogers R, Smith P, 2004). The amphibole mineral are chemically more stable and are biopersistent with half-lives ranging from a few years to a lifetime.
Only 3 of the asbestos minerals have had significant commercial use: chrysotile (white asbestos), crocidolite (blue asbestos) and amosite (brown asbestos). By far the most commonly used type was and is chrysotile, comprising 90% of all asbestos used in the built environment. Amphiboles, because of their danger to health, are little used today and have been banned in most countries for many years. Chrysotile is still in common us in many countries, largely because, of the six types of minerals, it poses by far the least risk to human health.