8. Chrysotile asbestos
Chrysotile is the most widely used asbestos variety, and is casually referred to as 'white' asbestos. It is a member of the group of minerals known as serpentine, all of which have the same composition - magnesium silicate.
Figure 8 Chrysotile asbestos
The serpentine group of minerals is widespread in nature: areas of northern Britain contain large quantities. Fortunately only the chrysotile variety occurs as a genuinely fibrous form and is much less common. Chrysotile is formed by hydrothermal alteration of rocks rich in magnesium; it may be dispersed in random orientation throughout the rock or occur in discrete veins as parallel or transverse fibres. In its raw state it is pale green, cream or white and it forms a fluffy mass of curly soft white fibres when processed. It is highly flexible and deforms inelastically which makes it ideal for spinning and weaving.
Chrysotile is a sheet silicate with alternate layers of SiO4 tetrahedra (linked in a hexagonal pattern), and Mg(OH) groups. Because of the mismatch in the dimensions of the two layers, stronger crystal structure is achieved by curvature of the composite sheets forming a scrolled structure with the Mg(OH) layer on the outside. This tubular form can be seen with high magnification transmission electron microscopy.
These tubes or 'fibrils' are the finest fibres of chrysotile that can be found. Their diameter is approximately 0.025 μm.
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