Washington — Constitution of Some Salic Silicates. 565 



Andesine ( Ab An ) \ (NaSi)AlSi 2 8 ) 

 Andesine, (At^An J, j (C aAl) AlSi 2 8 J 



f 8(NaSi)AlSi 2 8 ) 



Aneraousite, •] 10(CaAl)AlSi 2 O 8 V 



( l(Na,Al)AlSi,0 8 ) 



t . a •* /Ai a \ i l(NaSi)AlSi.,OJ 

 Labradonte, (Ab, An f ), j 2(CaAl)AlSi;o| \ 



In view of what has been said, it seems needless to point out 

 that all these feldspathic salts are of identical chemical type, 

 and are hence readily capable of isomorphous serial mixture, 

 as is typically seen in the plagioclases and hyalophanes. The 

 fact that they can all be referred to an orthosilicate formula, if 

 aluminum is regarded as purely basic, has been referred to 

 above. This, however, would seem to be a forced interpreta- 

 tion, and it is best to regard them all as salts of a (feldspathic) 

 acid, H 5 AlSi,0 8 , whose salts are polymorphous. As real 

 monoclinic symmetry of orthoclase would necessitate, on this 

 interpretation, that fellenadic acid be tetramorphous, it 

 simplifies the problem, and is in accord with recent views, to 

 eonsider it pseudomonoclinic. The salts of the general fel- 

 lenadic acid are thus considered trimorphous, represented by 

 triclinic anorthite, hexagonal nephelite, and isometric leucite. 



The behavior of the feldspars with regard to acids is charac- 

 teristic and significant. Orthoclase, microcline, albite, and 

 barbierite, with only the silicic integral (R'Si) present, are 

 unattached, while anorthite and carneoieite (?), with (R"A1) 

 present, are readily attacked, the former with production of 

 gelatinous silica. Anorthoclase and the sodi-calcic feldspars 

 follow the same rule, their resistance to acids increasing with 

 the content in molecules containing the (R'Si) integral. Celsian 

 and hyalophane, with the (BaAl) integral are only slightly 

 attacked or unattacked by acids, but the barium salts are 

 uniformly less soluble than the corresponding calcium ones. 



Leucite Group, isometric or pseudo-isometric. 



Leucite, (KSi) 2 (K„A1) (AlSi 2 8 ) 3 



"( wi(KSi) AlSi.O s ) 

 Psendoleucite, \ »(NaSi) AlSi„0 [ 

 ( ^(Na 2 Al) AlSi,0 8 \ 

 Analcite, (NaSi), (Na a Al) (AlSi.O.),4H a O 

 Maskelynite, (NaSi) (CaAl) (AiSi",0 B ) Q (?) 



The formula for leucite, as thus expressed, shows an iso- 

 morphous mixture in stoichiometric proportions of fellenadates 

 of two (KSi) molecules and one of (K„ Al). This complexity is 

 in accord with its great instability and rarity in rocks, and 



