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

 C S 3 + 3 (M, C,f, m n) S 2 



there is 1 atom of silica wanting. 



In all probability the mineral analyzed was a mixture of am- 

 phibole and some other magnesian mineral, containing a smaller 

 proportion of silica. 



5. Rock-Wood. 



The specimen selected for analysis was from the Tyrol. It 

 had much of the aspect of common asbestus. The colour was 

 yellowish-brown ; the texture was distinctly fibrous ; and the 

 fibres, from their disposition, gave the mineral a good deal of re- 

 semblance to wood. 



Opaque, soft. Specific gravity, 2.724. 



Its constituents were found to be, 



Silica, .... 54.920 



Magnesia, . . . 26.084 



Protoxide of iron, 12.600 



Alumina, . . . 1.640 



Water, .... 5.280 



100.524 

 This is equivalent to 



76 atoms silica, 

 29 atoms magnesia, 



7f atoms protoxide of iron r 



9, atoms alumina, 

 13 atoms water. 





