492 Eakle — Biotite-tinguaite Dike from Massachusetts. 



47-16 Na 2 Al 2 Si fl O 10 ) 



16-68 K 9 Al,Si 8 1B }■ 67*28 per cent feldspar. 



3-44 CaAl.,Si 2 8 ) 



9-61 Na 6 K 2 Al 8 Si n 3 . 1 ) 



8-09 H 4 Al 9 Si,O >■ 20*32 nepheline, kaolin and quartz. 



2-62 Si0 2 ) 



6-00 Na,Fe a Si 4 I3 [ 6-00 aBgirine. 



2-90 biotite. 



3-50 Fe 3 3 (FeMn)0| 6-40 biotite and iron oxides. 



100- 



The remaining minerals, sodalite, apatite, zircon and fluorite r 

 would probably form less than one per cent of the rock. The 

 same relative proportions of the minerals in a perfectly fresh 

 rock would require about one and one-half per cent more of 

 combined alkalies, with a corresponding decrease in the com- 

 bined silica and alumina. 



Mineralogical Laboratory, Harvard University, September, 1898. 



