A conventional description would include highly perfect cleavage, sub- 

 conchoidal to uneven fracture, vitreous to pearly luster, black, white, green, 

 brown and pink in color and with an uncolored streak. Pleochroism is strong, 

 with deeply colored varieties with absorption usually Z>Y>X (Dana, 1954). 



Mineralogically there are two main groups of asbestos minerals: ser- 

 pentine and amphibole. Common types, crystal class, chemistry and identi- 

 fication characteristics are given in Table 1. 



Water is considered an essential constituent of all types. Common fiber 

 lengths for all of the asbestos minerals are within the range of 0.2-10 ym 

 (ym = 10-6 meter). These values depend somewhat on the laboratory method 

 employed to disperse the fibers for measurement. 



For bulk analysis, the techniques of infrared spectroscopy, differential 

 thermal analysis and X-ray diffraction are employed. In order to study in- 

 dividual fibers, transmission electron microscopy, selected area electron 

 differaction and electron microprobe analysis methodology are employed. While 

 acceptance precision can be achieved through these expensive and time-con- 

 suming programs, the superiority of any one method has yet to be demonstrated 

 (Great Lakes Research Advisory Board, International Joint Commission, 1975). 



Geological Sources 



Chrysotile asbestos occurs in serpentine form that has been altered from 

 (a) ultrabasic rocks such as peridotite or dunite or (b) magnesium lime- 

 stones or dolomites (Bateman, 1950). The former occurrence yields about 90 

 percent of the world's asbestos supply. Amphibole varieties are found in 

 slates, schists, 

 pyroxenite. 



banded ironstones and as lenses and pockets in peridotite and 



TABLE 1. CLASSIFICATION OF ASBESTOS. DATA FROM GREAT LAKES RESEARCH 

 ADVISORY BOARD, INTERNATIONAL JOINT COMMISSION, 1975 



Group 



Name 



Chemistry 



Crystal 



Characteristics 



Serpentine 



Chrysotile 



(Mg,Fe) 2 Si0 4 ] 



Monoclinic 



Hollow Curved Fibers: 

 0D^250 A; ID^SO A; of- 

 ten occur in bundles 

 and change shape in 

 lung liquids, 



0D>2500 A 



Amphibole 



Anthophyllite 



Amphibole 



Amphibole 



Cummingtonite^ 



Grunerite* 



(Mg,Fe 

 (Mg,Fe 



)SiOT] 



Orthorhombic 



WOT] 



Monoclinic 



Amphibole 



Tremolite** 



(Fe,Mg)SiO^] 



Monocl inic 



(Ca,Mg)Si 4 n 



Monoclinic 



*That particular amphibo e gener 

 Mining Company tailings dischar 

 **That particular amphibole found 

 Superior. 



Straight: 

 do not oc- 

 cur in bun- 

 dles and do 

 not split or 

 change shape 

 in lung liq- 

 uids 



0D>1500 A 



0D>1500 A 



0D> 600 A 



aTTy released into Lake Superior by Reserve 

 ge of 67,000 tons/day. 

 in natural lacustrine sediments of Lake 



134 



