Washington — Kaersittite from Linosa and Greenland. 203 



Na— O x /O— Na 



\Si_0— Si< 



/ o o \ 



Fe— O x | | /O— Fe 



\ o >si-o-s< o / 



If we assume then the presence of the bases Na 2 and 

 (Fe,Al) 2 O s , which will form the metasilicates JSTa 2 Si0 3 and (Fe,- 

 Al) 2 Si 3 6 9 respectively, the composition of our amphiboles may 

 be calculated as follows, the presence of some of Penfield's 

 radicals being needed to account for the F and H 2 and the 

 excess of R 2 3 over the alkalies. The distribution can be made 

 mathematically, so that the whole will conform to the meta- 

 silicate formula, by the use of equations analogous to those 

 used in the calculation of the norms of igneous rocks.* 



Linosa. Kaersut. 



[(Al, Fe) 2 3 (F, OH)J Si0 3 . 



(Al,Fe) 2 3 R] Si0 3 . 



(Al,Fe) a 3 ^ 8 ]Si0 3 ._..- 

 Na(Al, Fe)Si 



•017 



•088 



•039 

 •009 

 •273 ) 

 •217 j 



•490 

 •490 



•033 

 •026 

 •04'4 

 •015 



(Mg,Fe) (Al,Fe) 2 Si 4 12 ... 



(Mg,Fe)0... 



CaO ..... 



Residual SiO„ 



•429 

 •195 



•624 

 •625 



Assuming that the amphiboles are metasilicates, as is held 

 by most authorities, and which view is greatly strengthened 

 by the work of Penfield and Stanley, it is clear that the com- 

 position of the hornblendes of Linosa and Kaersut may be 

 rationally explained by the assumption of the presence of mole- 

 cules of the general type (R' 2 , R") R'" a Si 4 ]2 . The presence 

 of these molecules also seems to be quite unavoidable in the 

 case of such amphiboles as riebeckite and glaucophane, and 

 furthermore they cannot be interpreted only in terms of biva- 

 lent radicals such as those suggested by Penfield and Stanley, 

 though some of these may be assumed to be present. 



The two authors mentioned do not discuss the question of 

 the presence of such riebeckitic molecules, an omission unhesi- 

 tatingly to be ascribed to the preliminary and, most sadly, 

 unfinished character of their paper. Such a discussion would 

 have been inevitable had their investigation been extended to 

 the glaucophanes, riebeckites, and other highly sodic amphi- 

 boles, as one of us knows to have been the late Professor Pen- 

 field's intention. So far as can be learned from the published 



* Cross. Iddings, Pirsson, and "Washington, Quantitative Classification of 

 Igneous Bocks, Chicago, 1903, pp. 194, 195. 



