64 



UNITED STATES MINERAL RESOURCES 



Jenkins (1949, 1960), which are complementary in 

 their coverage, are recommended. Condensed com- 

 parisons of worldwide scope of subjects such as 

 mining and milling methods, grading and classifica- 

 tion, and production and consumption trends have 

 been furnished by Bowles (1959). Updated discus- 

 sions of trade and use trends are available in two 

 articles in Industrial Minerals (1970a, b). 



DEFINITION AND PROPERTIES 



"Asbestos" is a term applied in commerce to 

 naturally fibrous silicates that are amenable to 

 mechanical separation into fine filaments of con- 

 siderable tensile strength and flexibility; these 

 fibers have, by virtue of unique combinations of 

 physical and chemical properties, a great variety 

 of industrial uses. Manmade fibers and naturally 

 occurring organic fibers do not possess the full range 

 of properties inherent in asbestos, and thus — at 

 best — can be substituted only partially for the min- 

 eral fibers (Carroll-Porczynski, 1958). Chrysotile, 

 the fibrous form of serpentine, constitutes about 93 

 percent of world asbestos production. The other 

 five asbestiform minerals ordinarily used are am- 

 phiboles. In order of quantities consumed, they are : 

 crocidolite and amosite, which respectively make up 

 about 31/2 and 2V2 percent of asbestos commerce; 

 anthophyllite and tremolite which probably make 

 up only a fraction of 1 percent of the asbestos used ; 

 in recent decades, actinolite, the least used, has 

 seldom been given note in the trade. These use ratios 

 mainly reflect desirable physical properties; croci- 

 dolite and amosite do have particular properties that 

 would favor greater use if they occurred more uni- 

 versally and in larger amounts. 



The properties primarily of concern in evaluating 

 asbestos as to ultimate use are: (1) flexibility, (2) 

 length of fiber, (3) tensile strength, (4) chemical 

 reactivity, (5) resistance to heat, (6) electrical 

 conductance, and (7) filtration characteristics. (See 

 Badollet, 1951 and 1953, for comparative properties 

 of asbestos species.) The use of a given lot of asbes- 

 tos is governed by acceptable properties which are 

 determined largely by fiber length. The longest fibers 

 demand the highest prices and the shorter grades 

 progresively are lower in value. (In recent years 

 soft chrysotile fibers %-inch long have sold for 

 $1,500-$1,600 per ton, whereas the shortest grades 

 have brought $50-$100 per ton.) Thus, asbestos 

 should be separated from the parent rock, fiberized, 

 and classified by length with attention given to a 

 minimum of breakage. 



By virtue of variations in physical properties, a 

 given mineral is put to very different uses. Soft, 



silky chrysolite of adequate length fabricates into 

 textiles. The same fiber, because it forms a slurry 

 that can be dewatered only slowly, is unsuitable for 

 processing as the binder in cement products. Harsh- 

 ness — that is, resilience like a broomstraw when 

 flexed — makes chrysotile very unsuitable for textile 

 use but greatly enhances the manufacture of chryso- 

 tile into asbestos-cement products. Some desirable 

 combinations of properties are limited in occur- 

 rence. An example of strategic concern is textile- 

 quality chrysotile of low iron content for heat- 

 resistant electrical insulation. Physical characters 

 ordinarily overlooked can be significant. Resources 

 recently developed near Coalinga, Calif., are illustra- 

 tive. For decades large parts of an extensive ser- 

 pentine mass in this area had been recognized in 

 the form of minutely sheared incoherent leathery 

 flakes, quite lacking resemblance to typical asbestos 

 ores. On appraisal in the late 1950's, the flaky ma- 

 terial proved to contain high proportions of micro- 

 scopic fibers, all of the shortest lengths ordinarily 

 recovered in the processing of ordinary ores. Fur- 

 ther, these fibers had special attributes of being 

 superior in whiteness — thus being particularly 

 suited as binders for floor tiles — and of capacity to 

 absorb hydrocarbons. 



USES 



Asbestos is widely stated to be a constituent in at 

 least 3,000 manufactured products. It is a particu- 

 larly critical material in friction materials and in 

 electrical insulation, where resistance to moisture, 

 flexure fatigue, and abrasion and a capacity to 

 absorb resins can be as important as heat and flame 

 resistance. Asbestos is important as an abrasion- 

 and corrosion-resistant binder or reinforcing mate- 

 rial in products made of rubber or plastic and mixed 

 with lubricants or other compounds used in packings 

 or gaskets, where an inert material is required ow- 

 ing to exposure to superheated steam, acids, alkalis, 

 oil, or seawater. Laminated as paper or in textiles, 

 it is fabricated into products that are immune to 

 attack by fungus, bacteria, or vermin and that are 

 not affected by alternate wetting and drying. Asbes- 

 tos fibers can be finely divided ; and, separated in 

 optimum degrees, they are superior inert mediums 

 for filtering gases and liquids. This partial listing 

 only superficially indicates the many asbestos- 

 bearing products essential to our modern way of 

 life ; actually such products account for less than 

 one-third of asbestos consumption. 



About 70 percent of U.S. and world consumption 

 of asbestos is in asbestos-cement products. Indeed, 

 the demand for shingles, roofing, wallboard, flat and 



