DR T. THOMSON on Asbestus, Chlorite, and Talc. 355 



bases, all of which are in combination with silica. The atoms 

 of silica being 35, and those of the bases only 21^, it is clear 

 that some of the bases must be in the state of simple silicates, 

 and others in that of bisilicates. If the magnesia be a bisilicate, 

 while the lime, protoxide of iron, and alumina, are simple sili- 

 cates, then all the atoms, both of the silica and bases, will be in 

 combination. So that we might consider amianthus as compo- 

 sed of, 



13^ atoms bisilicate of magnesia, 

 5 atoms silicate of lime, 

 2 atoms silicate of iron, 

 1 atom silicate of alumina. 



But, if we compare the constituents of amianthus with the 

 numerous analyses of amphibole given by BONSDORF, in his in- 

 structive paper upon the chemical constitution of that compli- 

 cated mineral species, we cannot avoid seeing a very close re- 

 semblance. Now, pure amphibole is composed of C S 3 -f 3 M S 2 . 

 But it would appear from the researches of BONSDORF, that 

 part of the silica is occasionally replaced by alumina, and part of 

 the magnesia by protoxides of iron and manganese. If we ad- 

 mit these substitutions in the present case, we shall have, 



36 atoms of silica and alumina, 

 15.5 atoms magnesia and protoxide of iron, 

 5 atoms lime. | 



This is equivalent to, 



7.2 atoms silica and alumina, 



3 atoms magnesia and protoxide of iron, 



1 atom lime. 



VOL. XI. PART II. Y y 



