140 RE-EXAMINATION OF AMERICAN MINERALS. 



From these is deduced the oxygen ratio for the protoxides, 

 peroxides, and silica, 1 : 4 : 10, and the formula R 3 Si 2 +4X1 Si2 ? 

 corresponding with the results recently obtained by Eammels- 

 berg* for the composition of the spodumene from Uton and 

 the Tyrol. The silica, however, is somewhat lower than that of 

 the European specimens, which is probably owing to the greater 

 purity of the American mineral, it being found in crystals. 



Since completing the above examination of the spodumene 

 from Norwich, we have noticed a recent examination of the 

 variety from Sterling, Massachusetts, by Eammelsberg, in 

 which he states his having found 4.5 per cent, of potash, and 

 a ratio nearer 1 : 5 : 12 than 1:4:10. This difference is ac- 

 counted for by that author on the ground that the mineral is 

 somewhat decomposed, and that the original ratio was 1:4:10. 

 The fact is Eammelsberg did not examine the pure spodumene 

 from Sterling, as will be seen by his own account of the 

 specimens analyzed. They were white, yellowish, or bluish 

 gray in color, possessing little luster, penetrated with small 

 fissures, and in these fissures, as well as in many places on the 

 surface, were scales of mica with yellow flakes of oxide of iron ; 

 the specific gravity was 3.073. Now the spodumene, as we 

 have procured it perfectly pure from Sterling, Massachusetts, 

 is of a greenish-gray color, fine luster, and very compact, 

 cleaving with perfection, a specific gravity of 3.182, and with 

 a composition according perfectly with the requirements of the 

 ratio 1:4:10, containing even a little more lithia than the 

 variety from Norwich. In an early examination by Brush, 

 published several years ago, the silica was given too low, he 

 not having separated the small amount of silica always asso- 

 ciated with the alumina. A recent analysis gives as the com- 

 position of this spodumene : 



Oxygen ratio. 



Silica 64.50 33.41 or 10.66 



Alumina 25.30 1 12.54 or 4 



Peroxide oi iron 2.55/ 



Lime 431 



S£!:;:::z::::::::: ^ 8 -« ot1 - ot 



Potash and soda 1.10 J 



Loss by ignition 30 



99.89 

 * Pogg. Ann., lxxxv, 544. 



