Dft T. THOMSON'S Analysis of some Minerals. 

 Or we may state the composition this way : 



3 atoms sulphate of alumina, . 21.75 

 1 atom sulphate of soda, ... 9-0 

 20 atoms water, . .... . . 22.5 



53.25 



The only difference between native and artificial soda-alum 

 is in the water of crystallization. In the former it amounts only 

 to twenty atoms, while in the latter it is twenty-five atoms. 

 Artificial soda-alum crystallizes in regular octahedrons like com- 

 mon alum. But the native seems to crystallize in prisms. At 

 least that is the natural inference from its fibrous structure. I 

 made some attempts to obtain it in more regular crystals, but 

 they were unsuccessful, owing, I believe, to the heat of the 

 weather when the trial was made. 



IX. Siliceous Hydrate of Magnesia. From Haboken, New 

 Jersey. Nemalite of NUTALL. 



This mineral was sent me some years ago by Mr NUTALL, 

 among many other interesting magnesian minerals from the same 

 locality of which he had some time before given an account to 

 the American public. 



The mineral which I am going to describe occurs in veins in 

 serpentine, and was taken for amianthus till its true nature was 

 discovered by Mr NUTALL *. 



The colour is white, with a slight shade of yellow. 



Composed of elastic fibres, easily separable, and bearing a 

 striking resemblance to the fibres of amianthus. 



* See SILLIMAN'S Journal, iv. 19. 

 yr .51 TJIA1 .IX .JtOV 



