﻿82 



Canadian Record of Science. 



1152 



1202 



2356 



2354 



The atomic and (luantivalent ratios deducible from the 

 above analysis are as follows : — 



Atomic. Quantivalent. 



Si 570x4 = 2280 ) 2356 



Ti 19x4= 76 [ 



Al 226x3 = 



Fe"^ 158x3 = 



Fe" 305 X 2 = 



Mn 9x2 = 



Ca 176x2 = 



Mg 34x2- 



K 48 



Na 106 



The ratio of (R,0 + EO) : R,03 : SiO, is 601 : 192 : 589, 

 or approximately 3:1: 3„ and obviously the mineral is 

 a true orthosilicate agreeing fairly with the formula 



(RgPOs R„Si30,,, or, more fully, (Fe, Mn, Ca, Mg, K^, 

 Na,)^ (Fe, Ai)2 ( Si, Ti)3 O^o— a constitution analogous 

 to that of garnet. 



So far as we are aware no other hornljlende containing 

 so small a proportion of silica has been analyzed ; but the 

 small percentage of silica is explained l)y the large pro- 

 portions of ferrous and ferric oxides. This is made plain 

 by the following formulae and the corresponding percent- 

 ages of silica deduced from them : 

 Formula. 

 3FeO, Fe^Os, 3Si02 

 3CaO, Fe^Oa, 3Si02 

 3FeO, Al.Oa, 3Si03 

 3Na,0, Al^O,, 3SiO, 

 3CaO, AI2O3, 3SiO, 

 The Dungannon hornblende is interesting in connection 

 with the views of Scharizer, who suggested in 1884^ that 

 many of the aluminous hornblendes might be regarded 

 as molecular compounds of the metasiHcate actinolite, 



1 N. Jahrb. f. Min., 1884, ii, p. 143. 



P.C. of SiO, 

 3219 

 35-43 

 36-14 

 38-38 

 40-00 



