THK NONMETALLIC MINERALS. 



297 



S=:?>i 



...I 



I 



Fig. 10. 



ASBESTOS FIBERS. 



After G. P. Merrill. 



Cheniically thi.s is ii normal iiietasilicate of magnesia of the formula 

 (Mg'.Fe) 8iO.,, ditfering, it will be observed, from asbestos proper in 

 containing no appreciable amount of lime. It further ditt'ers in crys- 

 tallizing in the orthorhombic rather than the monoclinic system, a 

 feature which is determinable only with the aid of a microscope. 



The shape and size of the 

 libers is essentially the same 

 as true asbestos. The fibrous 

 variety of serpentine to which 

 the name asbestos is commer- 

 cially given is a hydrated met- 

 asilicate of magnesia of the 

 formula H^MggSiaOg with usu- 

 all}^ a part of the magnesia 

 replaced by ferrous iron. It 

 differs, it will be observed, 

 from asbestos and anthophyl- 

 lite in carrying nearh" 14 per 

 cent of combined water and 

 from the first named in con- 

 taining no lime. This mineral 

 is in most cases readily distin- 

 guished from either of the others by its soft, silk-like fibers and further 

 by the fact that it is more or less decomposed by acids. As found in 

 nature the material is of a lively oil yellow or greenish color, compact 

 and quite hard, but may be readily reduced to the fluft'y, fibrous state 

 by beating, handpicking, or running between rollers. The length of 

 the fiber is quite variable, rarely exceeding 6 inches, but of very smooth 

 uniform diameter and great flexibility. 



The mineral crocidolite, although resembling somewhat fibrous ser- 

 pentine, belongs properly to the amphibole group. Chemically it is 

 anhydrous silicate of iron and soda, the iron existing in both the sesqui- 

 oxide and protoxide states. More or less lime and magnesia maj" be 

 present as combined impurities. The color varies from lavender blue 

 to greenish, the fibers being silk}' like serpentine, but with a slightly 

 harsh feeling. The composition of representative specimens of these 

 minerals from various sources is given in the accompanying table. ^ 



' From Notes on Asbestos and Asbestiforni Minerals by George P. Merrill, 

 ceedings of the U. S. National iNIuseuni, XVIII, 1895, pp. 281-292. 



Pro- 



