24 CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. [bull. 167. 
account for so great a divergence. If we consult otlier analyses, as 
we find them tabulated in manuals like those of Dana and of Hintze, 
we shall find other cases resembling this, and also examples of vari- 
ation in the opposite direction, with silica low and an apparent excess 
of bases. Most analcite gives quite sharply the metasilicate ratios 
required by the accepted formula; but the variations from it are large 
enough, common enough, and regular enough to command attention. 
The analyses are not all covered by the recognized theory, and the ap- 
parent irregularities are not fortuitous, but are systematic in character. 
One explanation of the seeming anomalies is simple and clear. If 
analcite, instead of being a metasilicate, is really a mixture of ortho- 
and trisilicate, then all of the analyses became intelligible. In most 
cases the two salts are commingled in the normal ratio of one to one; 
but in our analcite the trisilicate predominates, while in some other 
samples the orthosalt is in excess. All reduce alike to the simple 
expression 
NaAlX. H 2 0, 
in which X represents nSi04 + mSi 3 8 ; a formula which agrees with 
evidence from various other sources. 
For example, analcite may be derived in nature either from albite, 
AlXaSi 3 8 , or nephelite, AlNaSi0 4 , and, on the other hand, alterations 
of it into feldspars have been observed. Its closest analogue, leucite, 
has yielded pseudomorphs of orthoclase and elaeolite; while leucite and 
analcite are mutually convertible each into the other. The evidence 
of this character, the evidence of relationship between analcite and 
other species, is varied and abundant, and the simplest conclusion to 
be drawn from it is that which has been given. Every alteration, 
every derivation, every variation in the composition of analcite points 
to the same belief. The consistency of the data can not well be denied. 
In the case of a normal analcite — that is, one which conforms to the 
usual empirical formula — the expression which best represents these 
relations is 
Al 4 Na 4 (Si0 4 ) 2 (Si 3 8 ) 2 . 4H 2 0; 
and this accords with the minimum molecular weight as determined by 
the study of our ammoniated residue. Structurally, this is comparable 
with the formula? of garnet, zunyite, sodalite, nosite and leucite; all of 
which are also isometric in crystallization. The more important of the 
symbols are as follows: 
Si0 4 =Ca Si0 4 =Na, Si0 4 =Na 
^>Ca ^>A1-C1 \u-so,-Na 
Al- — Si0 4 =Ca Al— SiO.^Na, Al' Si0 4 =Na. 
X Si0 4 =Al Si0 4 =Al X Si0 4 E=Al 
Garnet. Sodalite. Nosite. 
