DR T. THOMSON on Asbestus, Chlorite, and Talc. 369 



The water, silica, and peroxide of iron, are probably all com- 

 bined with the magnesia, constituting in all probability 



5 atoms silicate of magnesia, 

 1 1 atoms bihydrate of magnesia, 

 1 atom ferrate of magnesia. 



Were we to consider the peroxide of iron as replacing a por- 

 tion of silica, the constitution of nemalite would be 



1 atom silicate of magnesia, 



2 atoms bihydrate of magnesia ; and its symbol would be 



MS + 2 MA? 2 . 

 4t 

 Nemalite, therefore, constitutes a new species of magnesian 



minerals, which may be distinguished by the name of hydro-sili- 

 cate of magnesia. 



The marmolite of NUTALL, found in the same place with his 

 nemalite, would seem, from the analysis of NUTALL, to be a hy- 

 drous silicate of magnesia, composed of MS + lAq. But I find, 

 by a careful analysis of some specimens of it, for which I am in- 

 debted to the kindness of Professor NUTALL, that its composi- 

 tion is exactly the same with the picrolite of HAUSSMAN, or the 

 precious serpentine of other mineralogists. Precious serpentine 

 is composed of 



1^ atom silica, 

 1 atom magnesia, 

 1 atom water ; 



V.V.; : : ', '* 



Or it is a hydrous sesquisilicate of magnesia. 



