DR T. THOMSON on Asbesfus, Chlorite, and Talc. 377 



It is obvious at once, that talc-slate consists essentially of 

 MS 2 + MS 3 ; but that it is mixed also with a small quantity of 

 silica, lime, alumina, protoxide of iron, and water. These bodies, 

 in all probability, are not chemically combined, but merely me- 

 chanically mixed with the pure talc ; thus disguising its exter- 

 nal character somewhat. The slight difference in the specific 

 gravity probably depends upon the laminated texture of the talc. 



3. Potstone from Sweden. 



I got the specimen which I subjected to analysis from my 

 friend Mr LORANG of Gottenburg. It was polished, which pre- 

 vents me from describing its characters with much accuracy. 

 When examined with a glass, it exhibited a mixture of small sil- 

 very plates, like talc, and black-looking crystalline grains. It 

 was opaque ; the hardness nearly that of talc ; the specific gra- 

 vity 2.88. It was sectile, and bore a considerable resemblance 

 to a mineral which I have seen described by the Wernerians un- 

 der the name of Chlorite-slate. Its constituents were as follows : 



Silica, 49.01 



Magnesia, 30.20 



Protoxide of iron, . . 11.40 



Alumina, 6.08 



Water, 4.20 



100.89 

 This is equivalent to, 



5 atoms silica, 

 2 atoms magnesia, 



i atom protoxide of iron, 



\ atom alumina, 



f atom water. 



