104 



Cincinnati Society of Natural History. 



tion of Professor F. W. Clarke, of the United States Geolog- 

 ical Survey, with the following result : 



Si 2 , . . . ; . . J ;. ' 50.17 



Ti 2 55 



Al 2 3 , . . . .... 27.97 



Fe 2 3 , : Ur. 3 > . 6.13 



■PeO, .hirU, . ii i.^V..:Uv>..«:* .... \ . S! - . I.l8 



Mg O... , ...... r i.t 5 



K 2 O . : . -» 7 77 



Na 2 O . ... . . . . 48 



Water below ioo°, 42 



Water above ioo° 3.94 



P 2 5 , v"^;* . . S v 06 



Total 99 82 



This analysis represents, approximately, the following per- 

 centages of constituent minerals : 



Muscovite . . 72.7 



Quartz, 17.3 



Magnetite and Iron Hydroxide, 8.4 



Other impurities (rutile, apatite, etc.), 1.6 



Total 100.0 



According to the recent analyses of Penfield the composi- 

 tion of fresh staurolite has been established as either Al 

 (Si0 4 ) 2 (A10H) 4 (FeOH) or Fe (Si 4 ) 2 (A10H) 5 . The 

 breaking down of this mineral into muscovite, with the 

 separation of iron hydroxide and the loss of alumina, speaks 

 in favor of the first of these formulae. The theoretical com- 

 position of the two minerals are as follows : 



Staurolite. Muscovite. 



H Al 5 Fe Si , 13 . 





(KH) Al, Si 2 0,. 





Si 2> 



26.32 



Si 2 , ; 



45-2 



Al 2 O a , 



• 55-92 



Al 2 3 , 



385 



FeO, : . . 



15 79 



K, O, 



1 1.8 



H 2 O, 



1.97 





4-5 



Total 



100.00 



Total 



100.0 



