﻿1 68 SMITH. 



According to Merrill, 1 " there are four varieties of mineral substances 

 coming under the general term of "asbestos." There are : 



1. True asbestos. 



2. Anthophyllite. 



3. Chxysotile (fibrous serpentine). 



4. Crocidolite. 



Physical characteristics. — From Merrill's Non-Metallic Minerals. 



Asbestos. — The true asbestos is of a white or gray color, sometimes greenish 

 or stained yellowish by iron oxide. Its fibrous structure is, however, its most 

 marked characteristic, the entire mass of material as taken from the parent rock 

 being susceptible of being shredded up into fine fibers sometimes several feet in 

 length. In the better varieties the fibers are sufficiently elastic to permit of 

 their being woven into cloth. Often, however, through the effect of weathering 

 or other agencies, the fibers are biattle and suitable only for felts and other non- 

 conducting materials. The shape of an asbestos fiber is, as a rule, polygonal in 

 outline and of quite uniform diameter; often, however, the fibers are splinter-like, 

 running into fine needle-like points at the extremity. The diameters of these 

 fibers are quite variable, and, indeed, in many instances there seems no practical 

 limit to the shredding. Down to a diameter of 0.002 millimeter and sometimes 

 to even 0.001 millimeter the fibers retain their uniform diameter and polygonal 

 outlines. Beyond this, however, they become splinter-like and irregular as above 

 noted. 



The mineral anthophyllite, like amphibole, occurs in both massive, platy, and 

 fibrous forms, the fibrous form being to the unaided eye indistinguishable from the 

 true asbestos. 



Chemically this is a normal metasilicate of magnesia of the formula (Mg, 

 Fe)SiO ; „ differing, it. will be observed, from asbestos proper in containing no 

 appreciable amount of lime. It further differs in crystallization in the ortho- 

 rhombic rather than monoclinic system, a feature which is determinable only with 

 the aid of a microscope. The shape and size of the fibers are essentially the same 

 as true asbestos. The fibrous variety of serpentine to which the name asbestos is 

 commercially given is a hydrated metasilicate of magnesia of the formula 

 H 4 Mg 3 Si 2 9 with usually a part of the magnesia replaced by ferrous iron. It 

 differs, it will be observed, from asbestos and anthophyllite in carrying nearly 

 14 per cent of combined water and from the first named in containing no lime. 

 This mineral is in most cases readily distinguished 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 lively oil-yellow or greenish 

 color, compact and quite hard, but may be readily reduced to the white, 

 fluffy, fibrous state by beating, hand-picking, or running between rollers. The 

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

 uniform diameter and great flexibility. 



The mineral crocidolite, although somewhat resembling fibrous serpentine, be- 

 longs properly to the amphibole group. Chemically it is anhydrous silicate of iron 

 and soda, the iron existing in both the sesquioxide and protoxide states. More 

 or less lime and magnesia may be present as combined impurities. The color 

 varies from lavender-blue to greenish, the fibers being silky-like serpentine, but 

 with a slightly harsh feeling. 



"Merrill, G. P.: The Non-Metallic Minerals (1904), 181. 



