Asbestos fibers, types serpentine

It is important to recognize that asbestos is not a single substance, but is the generic name for a family of six related poly silicate fibrous minerals of which one (chrysotile) belongs to the serpentine family and five (actinolite, amosite, anthophyllite, crocidolite, and tremolite) belong to the amphibole family. These minerals differ from each other in physical and chemical properties, and each mineral can exist in a wide range of fiber sizes. These differences between fiber type and, more importantly, fiber size (length and diameter) are believed to be important determinants of the health risks posed by asbestos. 

ASBESTOS. The tenn asbestos is a generic designation referring usually to six types of naturally occurring mineral fibers which are or have been commercially exploited, These fibers are extracted from certain varieties of hydrated alkaline silicate minerals comprising two families seipe.ntin.es and amphiboles. The serpentine group contains a single fibrous variety chrysotile five fibrous forms of amphiboles are known anthophyllite, amosite, crocidolite. tremolite, and actinolite... 

Asbestos, the first inorganic fiber material used, is currently still exclusively produced from natural mineral deposits. It is formed by the hydrothermal conversion of basic and ultrabasic volcanic rock (olivine and pyroxene) to serpentine upon which the actual asbestos formation takes place leading to two asbestos sorts with different structures serpentine asbestos and amphibole asbestos. Asbestos can be produced synthetically by several hours heating of a polysilicic acid/metal oxide mixture (e.g. Mg, Fe, Co, Ni) in water at 300 to 350°C and 90 to 160 bar. The properties of four important asbestos types are summarized in Table 5.2-2. 

PHYSICAL PROPERTIES a group of six different minerals occurring naturally in the environment most common type is white others are blue, gray, or brown long thin fibers similar to fiberglass not volatile not soluble serpentine asbestos chrysotile mineral, strong, resistant to chemicals and heat amphibole asbestos brittle fibers, resistant to chemicals and heat... 

The serpentine form of asbestos, known as chrysotile, is mined chiefly in Canada and the former Soviet Union more than 90% of the asbestos used in the United States is in this form. The amphi-bole crocidolite is mined in small quantities, mainly in South Africa. The two minerals differ greatly in composition, color, shape, solubility, and persistence in human tissue. Crocidolite is blue, relatively insoluble, and persists in tissue. Its fibers are long, thin, and straight and they penetrate narrow lung passages. In contrast, chrysotile is white, and it tends to be soluble and disappear in tissue. Its fibers are curly they ball up like yarn and are more easily rejected by the body. Scientific studies of many types and by groups in many countries have shown that chrysotile asbestos is significantly less of a health hazard than other types. It is important to note that almost all manufactured materials in the United States contain only this form of asbestos. 

The primary useful property of phosphates that perhaps nothing else approaches, is the safety record of phosphates in manufacturing plants and households around the world. It was with this fact in mind that two candidates for new mineral fibers were chosen. There were at least eight other candidates that could have been selected. As noted, there are two general molecular forms of serpentine minerals that are referred to as asbestos. These are the chrysotile and the amphibole types. These two forms of asbestos are about as similar, chemically and physically, as sodium chloride and sucrose both are white crystalline solids. 

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