134 On the Chemical Composition of Wernerite, 
a third of what it is in seapolite; the quantity of magnesia 
is very small; that of soda less even than in meionite, while 
the quantity of potash is as great as in the generality of 
mica. In order to form an idea of the mode in which this 
mica has been produced, it is assumed that the original 
mineral in this instance was scapolite, whose composition 
agreed with the formula— 
(Na 0+2 CaO) 2 SiO, 4+ 2 (Al, O,, Si O,). 
which represents the composition of the Arendal Wernerite, 
and indeed almost all those from Scandinavia and America, 
which have been examined. Since the perfect Wernerites do 
not contain any, or at the most only a trace, of peroxide of 
iron, while the altered Wernerite always contains a more or 
less considerable quantity, it is allowable to infer that alumina 
is the only weaker base in the normal composition. By 
comparing this assumed original composition (1.) with that of 
the pseudomorphous mica, (II.) expressed centesimally with- 
out reference to the water, or carbonate of lime,— 
: I. 1, 
Silica, Gg 49-5 52-63 
Alumina, . 2 27:5 29-46 
Peroxide of iron, . 5:72 
Lime, Ss 15:0 2:52 
Magnesia, . . 0:43 
Soda, ay as Sy oh 5 , . . 2 8sS0 
Potash, . ge 94. 
100-0 100-00 
there appears a striking similarity between the proportions of 
silica and alumina in the two cases. Instead, however, of 
the soda in the original mineral, the mica contains almost 
exactly the same quantity of potash, besides a small quantity 
of soda. The original mineral would lose 12-48 per cent, of 
its mass, and receive in its place 5°72 peroxide of iron, 0°43 
magnesia, 1-3 soda, making together only 7°45 per cent.; and 
as the mica is denser than the generality of scapolite, the 
change would be attended with diminution of volume. 
Assuming, then, that in the production of this mica the re- 
lative proportion of silica and alumina suffered no alteration, 
the essential features of the change would be limited to— 
eT. ae a 
