abstracts: economic geology 287 



in the United States, but Arizona, Idaho, Virginia and Wyoming have 

 deposits of special interest. 



The fundamental property of asbestos is its fibrous structure, and 

 it includes the fibrous forms of several species of minerals, especially 

 amphibole and serpentine. 



Using the term "type of asbestos" to designate the form of fibrous 

 aggregation and "mode of occurrence" to designate the environment of 

 the asbestos deposit, referring especially to its relation to the rocks 

 with which it is genetically associated, there are three types of asbestos 

 and four modes of occurrence known in the United States. 



The three types of asbestos are cross fiber, slip fiber, and mass fiber. 

 The first occurs in veins and the fibers, if not disturbed since their for- 

 mation, run across the veins. The second occurs along planes of rock 

 fractures on which slipping has occurred, and the direction of the parallel 

 fibers in the slipping plane indicates the direction of the slipping. The 

 third occurs in the form of bundles or groups and the fibers may be 

 parallel or divergent. It is strongly contrasted with cross fiber and slip 

 fiber in that it forms the whole mass of the rock in which it is developed. 



Asbestos of the cross fiber type is almost invariably chrysotile (ser- 

 pentine) and rarely anthophyllite. Some of the slip fiber type is chryso- 

 tile but more is amphibole. The mass fiber type, so far as known, is 

 always anthophyllite in the United States. 



The first mode of occurrence is illustrated by the mines at Chrysotile, . 

 in the Lowell region of Vermont, where the productive serpentine belt, 

 so extensively mined in eastern Canada, reaches the United States. 

 There is a similar but less productive locality near Casper, Wyoming. 



An excellent illustration of the second mode of occurrence is in the 

 Grand Canyon of the Colorado in Arizona, where veins of high-grade 

 cross fiber chrysotile occur in a narrow belt of limestone. The limited 

 quantity and difficult accessibility hinders mining in that region. 



The third mode of occurrence as mass fiber (anthophyllite) is well 

 illustrated at Sail Mountain, Georgia, where though much less valuable 

 than chrysotile it has been mined for many years. There is a similar 

 deposit at Kamiah, Idaho. 



The fourth is illustrated by the slip fiber veins in the hornblendic 

 and pyroxenic rocks of Bedford City and Rocky Mount, Va., where 

 unsuccessful attempts to mine it were made some years ago. J. S. D. 



