Amphibole asbestos minerals

Table 2.4 lists the major amphibole mineral series and illustrates the chemical range of the group. The five commercial asbestos varieties are starred. Idealized chemical formulas for the amphibole asbestos minerals are as follows ... 

Monoclinic minerals have an inclined angle of extinction. Orthorhombic minerals have parallel extinction. Chrysotile can be monoclinic or orthorhombic depending upon whether it is the ortho or clino variety. The b axis of the clino variety is so close to 90° (93°), (25) that the fibers will appear to have parallel extinction unless this is carefully measured. Anthophyllite, an orthorhombic mineral, has parallel extinction that is, the angle of extinction is zero degrees. All amphibole asbestos minerals except anthophyllite are monoclinic. Although wollastonite is a triclinic mineral, its extinction is parallel, or nearly parallel. The angle of extinction of some asbestos minerals is shown in table I (26, 27). 

Sluis-Cremer GK, Bezuidenhout BN. 1989. Relation between asbestosis and bronchial cancer in amphibole asbestos miners. Br J Ind Med 46 537-540. 

The overall ehemieal eomposition of the amphibole asbestos minerals is also shown in Table 3. Amphiboles have a strueture that contains double chains of silicate tetrahedra, eross-linked with bridging eations attached to the hydroxyl groups. This strueture allows a wide range of eation replacement, which is reflected in the ehemieal eomposition and physieal properties of the amphiboles. The amphiboles are all more resistant to aeid than chiysotile and have a negative charge at physiologieal pH beeause of the ionizable silanol groups on the exposed silicate surfaee. 

Polymerization into (Si40,i) units gives rise to minerals characterized as having double chains. The configuration depicted in Fig. 2. IF is common and typical of the amphiboles, a mineral group of special interest because five amphiboles have been mined as asbestos. 

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. 

Two to 3 percent of the world s total asbestos production has been of the crocidolite variety, most of which has come from South Africa. Western Australia was a minor producer of crocidolite between 1944 and 1966. All amosite has been mined in the Transvaal Province of South Africa (2 to 3 percent of the world total). The only significant anthophyllite production came from Finland, where about 350,000 tons were mined between 1918 and 1966. Table 2.6 lists the composition, optical, and diffraction characteristics of the six asbestos minerals. More information on individual mineral species can be found in the references accompanying the sections on serpentine and amphibole types. Discussion of the geology, terminology, and exploitation of the several types of asbestos can be found in Ross (1981). 

The initial connection between asbestos and mesothelioma was made by Wagner et al. (1960), when all but one patient in a study of mesothelioma-related deaths were found to be miners, workers, members of their families, or others living in the area of South Africa where the amphibole-asbestos crocidolite was mined. A comparable occupational exposure to crocidolite has been documented in Australia, with similar results (Armstrong et al., 1984). Mann and his associates (1966) documented three cases of mesothelioma among fifty-four patients dying of pulmonary asbestosis, and in two of the patients the mesotheliomas were peritoneal rather than pleural. 

Actinolite-asbestos A type of amphibole-asbestos composed of the mineral actin-olite. See chapter 2. 

Amianthus A term from ancient times applied to the exceptionally long, silky, relatively fine, and highly flexible mineral fibers capable of being woven. The actual usage establishes that the term referred to amphibole-asbestos. No longer in common use in English, amianthus was occasionally used to refer to all types of asbestos. 

Amosite A commercial term for a type of amphibole-asbestos from South Africa consisting chiefly of fibrous members of the cummingtonite-grunerite series. Variable amounts of several fibrous members of the amphibole group and other minerals may be included in a particular sample. The name is an acronym derived from asbestos mines of 5outh Africa. 

Amphibole-asbestos A collective term for fibrous varieties of minerals in the am-phibole group. Types of amphibole asbestos are more closely identified (viz an-thopyllite-asbestos). Note that not all members of the amphibole group occur in fibrous form, and those that occasionally do may also be found in other habits (prismatic, columnar, blocky). 

Crocidolite-asbestos A trade designation for a specific type of amphibole-asbestos composed of the mineral riebeckitc. It is also called blue asbestos and, if obtained from South Africa, may be labeled cape asbestos. 

Hornblende-asbestos Obsolete synonym of amphibole asbestos. The term is derived from the early use of hornblende for the group of minerals now called amphiboles. Hornblende, defined today as a mineral series within the amphibole group, rarely occurs in fibrous form. 

Here alternate tetrahedra share two and three oxygen atoms, respectively, as in Figure 1.52(d). This class of minerals is known as the amphiboles (Figure 1.54), an example of which is tremolite, Ca2Mg5(0H)2(Si40n)2- Most of the asbestos minerals fall in this class. The repeat unit is Si40n ". ... 

In the double chains or ribbons, there are different kinds of tetrahedra sharing two and three vertices. The most numerous amphiboles and asbestos minerals, such as tremolite, Ca2Mgs(Si40n)2(0H)2, adopt the [Si40n] 6 doublechain structure, as shown in Fig. 14.4.9(f). 

It is interesting that the mode of cleavage of a silicate may reflect its structure. The asbestos minerals, which may be broken down into fibres, are related to the chainlike amphiboles, whereas the micas (composed of layers) may be easily cleaved to thin sheets. Crystals of the framework silicates are much more difficult to break, for they have chemical bonds extending over three dimensions. 

Harington, J.S. and Cilliers, J.J. le R., 1963. A possible origin of the primitive oils and amino acids isolated from amphibole asbestos and banded ironstone. Geochim. Cosmochim. Acta, 27 411-418. Harrison, C.G.D. and Peterson, M.N.A.-, 1965. A magnetic mineral from the Indian Ocean. Am. Mineral. 50 704-712. 

The geological or commercial meaning of the word asbestos is broadly applied to fibrous forms of the silicaceous serpentine and amphibole minerals mentioned above. Asbestos minerals form under special physical conditions that promote the growth of fibers that are loosely bonded in a parallel array (fiber... 

Asbestos fibers are basically chemically inert, or nearly so. They do not evaporate, dissolve, bum, or undergo significant reactions with most chemicals. In acid and neutral aqueous media, magnesium is lost from the outer bmcite layer of chrysotile. Amphibole fibers are more resistant to acid attack and all varieties of asbestos are resistant to attack by alkalis (Chissick 1985 WHO 1998). Table 4-2 summarizes the physical and chemical properties of the six asbestos minerals. 

Carter RE, Taylor WF. 1980. Identification of a particular amphibole asbestos fiber in tissues of persons exposed to a high oral intake of the mineral. Environ Res 21 85-93. 

Wylie AG, Verkouteren JR. 2000. Amphibole asbestos Ifom Libby, Montana Aspeets of nomenclature. Am Mineral 85 1540-1542. 

Asbestiform—Possessing the properties of asbestos. Minerals of specific chemical compositions can have asbestiform varieties that are fibrous in nature (e.g., crocidolite and amosite are the asbestiform varieties of the amphibole minerals, reibeckite and gmnerite tremolite and actinolite may be either asbestiform or nonasbestiform)... 

Regulatory agencies such as the U.S. Environmental Protection Agency (EPA) and Occupational Safety and Health Administration (OSHA) recognize six asbestos minerals chrysotile, a serpentine mineral and five amphibole minerals, actinolite asbestos, tremolite asbestos, anthophyllite asbestos, crocidolite asbestos, and amosite asbestos. Nonasbestiform amphibole minerals are not included in U.S. health regulations regarding asbestos because there is insufficient evidence that they will produce adverse health effects of the same type and severity produced by chronic exposure to asbestos. 

Nonasbestiform tremolite is the predominant form of tremolite in the earth s cmst, but there are many reports of tremolite asbestos occurring around the world in specific locations (including some locations in Maryland and California) and natural materials. Tremolite asbestos has only rarely been found in commercially mined deposits. It has never been a nationally important commercial source of asbestos in the United States. Two minerals of commercial importance that have been reported to contain tremolite asbestos or other amphibole asbestos are vermiculite and talc. 

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