Joly — On the Minerals of the Dublin and Wieklow Granite. 63 



muoh as 74 per cent, of beryl is obtained. This suggests that 

 only a small quantity of the oxide was removed in the process of 

 alteration. If we assume 58 per cent, of beryl present, then, on 

 Mallet's analysis, 7-59 per cent, of BeO is to be expected, leaving 

 2"16 per cent, of that body "free" or mixed through the ortho- 

 clase to the extent of 5 per cent, of its weight. 



It is also open for us to assume that the deficiency from the 

 normal percentage of BeO for the entire mass is due to weathering 

 only ; that, in short, none of the oxide was removed by the primary 

 alteration ; but that the subsequent weathering of the beryl con- 

 stituent into kaolin and the formation of a chloritic mineral are 

 alone accountable. On this hypothesis the orthoclase would con- 

 tain about 13 per cent! of BeO. We are, indeed, driven to suppose 

 that alteration had the effect of reducing the percentage of BeO, 

 at all events in some degree; for the examination of these crystals 

 goes to show that it is the beryl constituent which is most readily 

 kaolinized or replaced by chlorite ; and the analyses of kaolinized 

 beryl (Dana's min.) reveal a diminution or nearly complete re- 

 moval of glucina. 



The question, however, obviously cannot be discussed on the 

 results of one analysis only. 



Analysis of altered Beryl. 1 



Sp. gr., 2 



625. 



1 Made -with Mr. W. Early's kind assistance, and chiefly under his directions. 



