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



2. Talc-Slate. 



The mineral called Talc-Slate is obviously closely allied to 

 Venetian talc ; though there are many particulars in which the 

 external characters of the two differ. 



The specimen which I selected for analysis was from Novar- 

 da in Piedmont. 



Its colour was white, with a slight shade of yellow. Massive 

 and slaty. Composed of impalpable particles without any cleav- 

 age. Fracture flat conchoidal. Opaque, or only translucent 

 on the edges. Sectile, Lustre silky. Hardness about the 

 same as that of gypsum. Specific gravity 2.877. 



Its constituents were found to be, 



Silica, ...... 57.560 



Magnesia, .... 27.216 



Lime, 7.944 



* 



Alumina, 1.720 



Protoxide of iron, . . 4.716 

 Water, 1.600 



100.756 



This is equivalent to, 



5 atoms silica, 



2 atoms magnesia, 



0.21 atom silica, 



0.41 atom lime, 



0.14 atom alumina, 



0.19 atom protoxide of iron, 



0.25 atom water. 



