Van Orden, D.R., Allison, K.A., Lee, R.J., Differentiating Amphibole Asbestos from Non-Asbestos in a Complex Mineral Environment, Indoor and Built Environment, Vol. 17, No. 1, 2008, p. 58-68.
Abstract
Extending the TEM methods designed for the evaluation of atmospheres in which any primary mineral fibers present are derived from a commercial asbestos fiber is a challenging task. This is because the methods employed leave it to the expertise of the user to identify and evaluate interferences. Improper analysis of nonconstruction materials for asbestos content often results in the misidentification of non-asbestos amphibole particles as asbestos fibers. These errors have received widespread publicity in the media (such as the asbestos-in-crayons story) and have caused unwarranted reformulation of harmless products. The primary cause of these errors has been a poor understanding of mineralogy and analytical techniques among the many asbestos laboratories that arose following the passage of the ‘Asbestos Hazardous Emergency Response Act’ (AHERA) regulations. This study outlines a procedure based on published data that can be used to correctly and five varieties of amphibole fibers (anthophyllite asbestos, tremolite asbestos, actinolite asbestos, crocidolite, and amosite) [1]. Serpentine is a sheet silicate, whereas the amphiboles are double chain silicate minerals. The six asbestos minerals are only a few of the nearly 400 minerals that can grow in a fibrous, or ‘asbestiform’, habit [2]. Commercial deposits of these minerals occur worldwide, but large-scale exploitation has been limited to only a few countries. Chrysotile was, by far, the most economically important asbestos mineral mined or used in the United States. Historically, 95% of the consumption of asbestos has been chrysotile, with minor amounts of amosite and crocidolite [3]. Anthophyllite and tremolite were also used in very limited quantities for specialty products, but actinolite had almost no commercial value. Other mineral fibers, which did not exhibit the physical, chemical, and thermal characteristics described above, had little or no commercial value and were not considered to be asbestos.The crystal habit of a mineral is the shape or form a crystal or aggregate of crystals takes during crystallization and is directly dependent on the environmental and geological conditions at the time of formation. The term ‘asbestiform’ is used to describe the unusual crystallization habit of minerals when the crystals form as thin, hair-like fibers, such as that which occurs with the six regulated asbestos minerals. The fibrous crystal habit is a less common form for amphiboles. The typical crystal habit of amphiboles is stubby prismatic. A prismatic crystal has one elongated dimension and two other dimensions that are approximately equal [4]. Cleavage refers to the preferential splitting of crystals along planes of structural weakness (cleavage planes) [5]. All monoclinic amphiboles have perfect (110) cleavage and orthorhombic amphiboles have perfect (210) cleavage [6]. Crushing or grinding of prismatic amphibole crystals may produce elongated particles that morphologically appear similar to asbestos, but do not possess the same unique physical properties.
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