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



made to come under the formula for amphibole. We must ad- 

 mit the alumina to replace a portion of silica ; and the protoxide 

 of iron partly to replace lime, and partly magnesia : 1^ atoms 

 replacing lime, and 5 atoms magnesia. The formula will be 



This variety of asbestus, then, like the preceding, is an am- 

 phibole. The water is probably only mechanically mixed, and 

 not a chemical constituent of the mineral. 



3. Asbestus, from Irkutzky, in Siberia. 



a * 



This specimen had a yellowish-white colour. It was com- 

 posed of long straight fibres, grouped together so as to give the 

 mineral the appearance of a congeries of imperfect prisms, in- 

 clined irregularly to each other. 



The fibres were easily separable from each other. They were 

 not elastic, and might be bent somewhat ; but were too frangible 

 to admit of being converted into threads. It is this want of 

 flexibility, together with a greater specific gravity, which consti- 

 tutes the principal distinction between common asbestus and 

 amianthus. 



Opaque or nearly so. 



Soft enough to be scratched by the nail. 



Streak white. 



Specific gravity 2.888. 



The constituents of this mineral, found by analysis, were as 

 follows : 



