50 THE CONSTITUTION OF THE SILICATES. [bull. 125. 
The micas in question occur in nature in great variety of admixture, 
and the corresponding vermiculites show a parallel complexity. In 
every case, however, the alteration of the one series into the other fol- 
lows the line indicated by the formulae, and the vermiculite is simply 
the mica with H in place of K or Na, plus 3 molecules of loosely com- 
bined water. Two of these molecules are, as a rule, given off at 100°, 
and regained in moist air, suggesting an analogy between the vermicu- 
lites and the zeolites. Some vermiculites, however, are only monohy- 
drated, and many of the so-called species which have received names 
are mere mixtures of altered and unaltered micas, representing stages 
of transition between the original mineral and the final product. 
Among the more characteristic vermiculites, kerrite, protovermiculite, 
hallite, and lennilite appear to be essentially trihydrated mixtures of 
the hydrophlogopite and hydroclintonite types, commingled in ratios 
nearly as follows : 
Hydrophlog. Hydroclint. 
Kerrite 5 : 1 
Protovermiculite 1 : 1 
Hallite 7 : 18 
Lennilite is near hallite, and both may contain small admixtures of 
chloritic material. The kerrite is quite near the typical hydrophlogo- 
pite alone. 
Jefferisite resembles protovermiculite in ratios, but with a hydrobio- 
tite in place of the hydrophlogopite ; that is, 
/Si0 4 =MgH /O 
/ h / >Mg 
Al— Si0 4 EEMgH. 3H 2 + Al— O * 3H 2 G 
^Si0 4 =Al \si0 4 =R' 3 
and vaalite is very nearly 
/Si0 4 =MgH /O 
/ / >Mg 
5 Al— Si0 4 =MgH. 3H 2 + 2 Fe— O & 3H 2 
^Si0 4 =MgH \si0 4 =MgH 
Maconite and lucasite are probably micas which have been partly 
vermiculitized, and an essential portion of the first-named mineral 
appears to be a derivative of muscovite. Eoseite is very near a mixture 
of partially muscovitic character, viz : 
7 Al— Si0 4 =Al. 3H 2 + 9 Al— O 3H 2 
^Si0 4 =Al \si0 4 =MgH % 
Each of these expressions gives the composition of its respective min- 
eral very closely, and so strengthens the general mica theory. The 
character of the alteration from a mica is simple, and is what is most 
reasonably to be expected. 
