DR T. THOMSON on Asbestus, Chlorite, and Talc. 371 



It is obvious at once that chlorite differs essentially in its 

 chemical constitution from all the varieties of asbestus. For 

 the atoms of sih'ca are to the atoms of the bases, with which it 

 must be united in the mineral, as 2 to 3. 



Chlorite is a compound of three subsesquisilicates, and, if we 

 suppose the subsesquisilicates of iron and magnesia to be pre- 

 viously in combination with each other, before they united to 

 the subsesquisilicates of alumina, the symbol for chlorite will be 

 as follows : 



Common chlorite, then, appears to constitute a peculiar mineral 

 species. 



2. Chlorite Earth. 



The specimen of chlorite earth, which I selected for analysis, 

 was given me many years ago by the Rev. Mr HEADRICK of 

 Dunnichen. He had picked it up somewhere in the Highlands 

 of Scotland, but I am not sure of the locality. It consisted of 

 small brown-coloured loose scales, having a silky lustre and a soft 

 feel. The specific gravity was 2.801. The constituents, after a 

 very careful analysis, which was twice made, were found to be as 

 follows : 



Sih'ca, .'.... . 48.166 



Alumina, ..... 16.851 



Peroxide of iron, . ". 19.100 



Potash, .;....' 6.558 



Magnesia, . . . . 2.916 



Lime, ...... 2.675 



Water, ..... 2.350 



98.616 



VOL. XI. PART II. 3 A 



