260 Chemical formulas of the Silicates. 
been attributed to alteration, and to impurities; and also by 
hers to a variation in chemical ratio analogous to that among 
the feldspars. I pass the subject without diemnalicte 
The species of Silicates which remain are the Feldspars and 
the Zeolites. The Feldspars may be regarded as unistlicate in 
anorthite ; bisilicate i in andesine and leucite; tersilicate in albite 
and orthoclas ase ; 1}-stlicate in labradorite ; ‘94. -silicate in oligo- 
clase. But this view would disband one of the most nat 
es in the series of feldspars _ oe foo “A lbite e, the forme cont 
Sit, aluminum and silicon, with the oxygen ratio 1: 3:4; and the latter sodium, 
aluminum and silicon, wi tio 1 sc ak bring: ext 
r one formula as follow atoms of oxygen in the 
bli 
of equivalents of aluminum and silicon aking silica as SiO?) in the two is the 
iS: ‘ ith i * 
number of atoms of proto: xyda is the s “The 2 ai the Al and Si 
in replaceable 1 for 1, and x, Ca, 1 for 1 eer Siemelas becom: 
shies Al? Si? git O18 ‘ 
orthite, Ca? Al? Al? Sit O18 : 
and are parallel thro’ cughout, The result looks well. But thi eege vente atom for 
atom, of a tetrad (Si) and a psendotriad (Al), and also of a monad (Na) and 
| ty. It takes two of a to re ror 
dyad (Ca), is an isap oui of a monad ad. 
ay be basic and replace aluminum it is impler method &: 
arriving at like formulas for the t in the ratio in which 
ate ‘ 
column contains the oxygen ratios, as ordinarily given: the second, the - same with 
part of the silica transferred to the bases and added to the alumina; the third, the 
resulting general ratio for the bases and silica 
Oxygen ratio, Oxygen ratio. Oxygen ratio. 
e R Si R Asi Si Bases : Silica. 
Anorthite; 1: 3:4 1:8+0:4 to ee 
Labradorite, 1:3: 6 1:841:5 1 1 
Andesite, Los: 8 1:84+2: ee 1 
Oligoclase 1:38:9 1: 8+ 25 : 6} 1 , 
Orthoctase,[ 1:8: 12 1:3+4+4:8 1 1 
mt ao oe reduced to Unisilicates, of the Anorthite and Garnet tyP® 
hem R, BAI, 7Si)a; | 
Fs » the following d be the special formulas of Anorthite, Labs 
pees - Si]0.1(¢R+48A1), 
habradorite, SifO,|(4(as, C + 
2 Albite. : Sif ,|(da, Ft Capa en 
fhe other maybe we writen inthe me mane. 
