RE-EXAMINATION OP AMERICAN MINERALS. 139 



ness 6 ; specific gravity 2.65 ; color flesh-red ; luster greasy ; 



structure massive. Chemical composition : 



Silica 44.46 



Alumina 30.97 



Peroxide of iron 2.09 



Lime 66 



Soda 15.61 



Potash 5.91 



Ignition 95 



100.65 

 From this we have the oxygen ratio for the silica, peroxides, 

 and protoxides, 9:6:2, and the formula E 2 Si-f 2£l Si. The min- 

 eral examined was furnished by Mr. Markoe, of "Washington ; 

 it is the one alluded to in our last paper as containing the 

 compact thomsonite, under the name of ozarkite. Since pub- 

 lishing the analysis of the latter we have procured a specimen 

 of the elseolite containing the thomsonite in handsome radiated 

 crystallizations. 



35. Spodumene. 



Several analyses of this species from Norwich and Sterling, 

 Massachusetts, were given by Mr. Eush in vol. x of American 

 Journal of Science and Arts. 



In these analyses the alkalies were determined as sulphates, 

 and from the amount of sulphuric acid the relative amount 

 of alkalies was calculated. Since these examinations it has 

 been found that this process is liable to great inaccuracy ; and 

 we have consequently made a re-examination with direct refer- 

 ence to this point ; it has been made altogether on the variety 

 from Norwich, which occurs in beautiful crystals. The results 

 of the re-examination show that the lithia and soda determi- 

 nations in the analyses referred to are erroneous. The method 

 used in this instance is that recommended by Rammelsberg — 

 the separation of the chloride of lithia from the chlorides of 

 potash and soda by a mixture of alcohol and ether. These 

 analyses gave 123 



Silica 64.04 63.65 63.90 



Alumina.. 27.84) 2g ^ 28J0 



Peroxide 01 iron .64 J 



Lime 34 .31 .26 



Magnesia trace trace trace 



Lithia 5.20 5.05 4.99 



|°f ?H .82 .80 



Potassa 16 J 



Ignition 50 .50 .60 



99.38 99.30 99.25 



