42 THE CONSTITUTION OF THE SILICATES. [bull.i* 
Here again no water is constitutional. In my former paper I assigne 
to both phillipsite and harmotome a hydration of 15 molecules but 1^ 
agrees better with the published analyses. In some cases the calciur 
of phillipsite is lower and the alkaline metals higher than is shown b, 
the ratio Ca 2 K 2 , but the ratio CaR' 4 does not appear to be reached 
unless by the presence of H among the components of R' 4 The gen 
eral formula for phillipsite and harmotome, as shown by all trustworth 
analyses, is A1 6 X 6 R" 3 .14H 2 0, when X represents Si0 4 +Si 3 8 and R 
is made to include the equivalent of the alkalies. Fusion experiment 
upon the two species seem to be wanting. 
To laumontite, CaAl 2 Si 4 I2 .4H 2 0, two constitutional formula?, ma^ 
be assigned, as follows : 
^Si0 4 =Al .Si0 4 ~Al 
Al_Si0 4 ZEAl Al-Si0 4 =H 3 
\si0 4 EICa \siO 4 =0a 
Ca +12H 2 Ca +4H 2 
I I 
,Si 3 8 =Ca /SiQ 4 =H 2 
Al— Si 3 8 =Al Al— Si0 4 ~H 3 
\si 3 8 HAl \si 3 8 =Al 
Both expressions give the same empirical composition, but the first 
is the more symmetrical. The second indicates a ratio between consti- 
tutional and crystalline water which agrees with the somewhat incom- 
plete recorded data, but the first is adjustable in such a manner as to 
represent the same facts. According to Doelter,* laumontite upon 
fusion gives anorthite, together with a pyroxenic mineral and an amor- 
phous ground mass, and this evidence may harmonize with either 
formula. A fuller experimental investigation of this species is evi- 
dently necessary. 
For the.isonietric faujasite the formula may be written structurally 
m two ways. One is in uniformity with the expressions assigned to the 
previous species, and is 
Al 4 (Si0 4 ) 4 (Si 3 8 ) 2 Ka 2 CaH 8 .15H 2 
The other is based upon the analcite formula, as developed in the pre- 
ceding chapter, thus : 
Si 3 8 =Na 2 
/ > Al - Si0 4 =H 2 . A1H,0 2 
Al— Si 3 8 =Ca + 15H 2 
Xx Si 3 8 =H 2 .AlH 2 2 
* Keues Jahrb., 1890, 1, p. 130. 
