Fibrous chrysotile

Chrysotile (serpentine) occurs in both clino and ortho stmctures. Both one-layer ortho and clino, and six-layer ortho (as in nacrite) stmctures have been observed. Chrysotile transforms at high temperature to forsterite [15118-03-3] and siHca. Particularly fibrous varieties are called asbestos (qv). 

In the 1987 Regulations, asbestos is defined as any of the following minerals crocidolite, amosite, chrysotile, fibrous anthophyllite, fibrous actinolite, fibrous tremolite and any mixture containing any of these. Before carrying out work on any substance suspected of being asbestos, a competent person must be called to advise on its possible... 

Asbestos is the name given to several different fibrous forms of silicates these go under names such as crocidolite, amosite, and chrysotile. These forms are, to varying degrees, also capable of eliciting fibrosis in lung tissue. In Chapter 6 it will be seen that some forms are capable of more serious damage - cancers of the lung and the mesothelium. 

The most important of these groups is the serpentine mineral group, because it includes the fibrous mineral species chrysotile, which is the most common fibrous mineral and the one most widely mined, processed, and manufactured as asbestos. 

Chrysotile is commonly fibrous whereas the other common serpentines, lizardite (a polymorph) and antigorite, are usually platy or massive, and rarely occur in fibrous forms. 

The individual cylindrical chrysotile fibrils undoubtedly contribute to the occurrence of this mineral species in fibrous form and may account for some of the flexibility and enhanced tensile strength of chrysotile fibers. Aveston (1969, p. 632) commented that asbestos was inferior [in tensile strength]... 

Chrysotile, sometimes called white asbestos, with its unique fibrous form, is an expression of the subtle structural variations that can be found in crystalline solids. These characteristics illustrate the need to go beyond the simple, or standard, chemical and crystal analyses used for identification, to understand the distinctive qualities of fibrous inorganic materials. 

Over the past several decades six different silicate minerals have been mined as asbestos and processed for industrial and commercial applications. The most commonly encountered asbestos mineral today is chrysotile. The five other minerals are tremolite, actinolite, anthophyllite, grunerite, and rie-beckite. All five are members of the amphibole group of minerals, and each can occur as chunky, acicular, or equant crystals, as well as in fibrous form. When found as fine fibrous aggregates, in quantities appropriate for mining, they are usually distinguished as a special variety—for example, tremolite-asbestos. 

Using in vivo techniques, natural and synthetic fibrous materials have been shown to induce fibrosis and carcinogenic responses that were directly related to dose, if the materials were placed on the target tissues. Chrysotile appeared to be more biologically active than the other UICC asbestos samples or fibrous glass, with particle size and shape having some influence on the response. In vitro experiments indicate that fibers can be cytotoxic and possibly mutagenic, increase the secretory activity of fibroblasts, and possibly initiate an immune cascade. 

Chrysotile A mineral in the serpentine group composed of hydrated magnesium silicate, which occurs in several crystalline modifications (see chapter 2) and usually in fibrous form. First described and named in 1834, chrysotile fibers were mined under the name serpentine-asbestos, or simply asbestos, long before that time. 

Serpentine-asbestos An early name for the fibrous form of serpentine rock that was mined. Today the term refers to chrysotile-asbestos. 

Chrysotile is a noncombustible fibrous solid that has been widely used as a fireproof thermal insulator, for brake linings, in construction materials, and for filters under the name of asbestos. It decomposes with loss of water at 600-800 °C, eventually forming forsterite and silica at 810-820 °C. Because it is more resistant to attack by alkalis than are the amphibole asbestoses, chrysotile has been used in chloralkali cell membranes and in admixture with Portland cement for making sewer pipes (Chapter 11). 

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