DR T. THOMSON on Asbestus, Chlorite, and Talc. 373 

 This is equivalent to 



30 atoms silica, 



t"> 7 I ' M "* T w 



13 atoms alumina, 

 2 atoms protoxide of iron, 



2 atoms lime, 



3 atoms potash. 



It is obvious that the atoms of silica are to those of the bases as 

 3 to 2. Hence all the bases must be in the state of sesquisili- 

 cates. 



From the analyses of KLAPROTH and ROSE, it appears, that 

 as the protoxide of iron in mica increases the alumina diminish- 

 es. If we take the atoms of alumina and protoxide of iron to- 

 gether, as also those of potash and lime, they are to each other 

 as 3 to 1. We may therefore consider the constitution of rhom- 

 boidal mica to be 



The atomic constituents of the chlorite earth are obviously, 



24 atoms silica, 

 1\ atoms alumina, 

 4 atoms peroxide of iron, 

 1 atom potash, 

 1 atom magnesia. 

 1 atom lime. 



Now, these proportions of silica and bases approach those of ses- 

 quisilicates. The mineral approaches, 



It belongs, therefore, to rhomboidal mica. Whether this be the 

 constitution of all the varieties of chlorite earth I do not know. 



3A2 



