62 Scheerer on Isomorphism. 
lime as 2 silicates. This would give us the formula thus modi- 
fied, 2(R)* Si+(R)* Sit. Schillerspar may therefore be looked 
upon as consisting of two atoms of serpentine and one atom of 
augite, And this is in accordance with the known fact, that the 
occurrence of schillerspar appears to be closely limited to forma- 
tions in which serpentine is met with. In the above oxygen ra- 
tio, the presence of *2°37 Gr, and of 1-28 to 1:73 Al, is not taken 
into account. What part these substances probably play in the 
composition of the mineral in question, will be broached as a con- 
jecture in the sequel. 
17. Crocidolite. (Stromeyer.) 
26-61 : 11-99 Se 
2661 : 11-40 t 3(R) 8i+-2(R)* Sit. 
(R) from two analyses =34-38 Fe, 2°48 Mg, 0-09 Mn, 0:03 Ca, 
7-07 Na, 4:80 H. The constituents are present in such propor- 
tions as would also admit of the formula, 3(R) Si+2 Fe? Si?. 
(KR) in this case comprehending the whole soda, water, and 
magnesia. Compare this formula with that of hornblende, 
R Si+R* Sis, : | 
Retinalite, Schweitzer’s “serpentine-like minerals” (to which 
forsooth, a general distinctive name should be given) and schiller 
spar, form therefore a peculiar group of minerals the formula of 
which consists of two other members, one of them being serpen- 
tine, and therefore containing water, while the other member 
consists of an anhydrous silicate, but which also contains, as in 
the former member, 1; 1 atomic bases. Crocidolite approaches 
a hydrous hornblende. nares es 
_ B. Silicates of magnesia and of other bases isomorphous there- 
‘with in combination with aluminates and oxydates of iron 
Chliorite and the minerals allied thereto. 
- 1. Chlorite. _ 
16°30 Si : 7-85 Al; 17-72(R ee eae 
isis i771 3 ieto” a(R)? Si+(R) Al 
The oxygen ratio here given, is calculated from the mean of 
five analyses, namely, two analyses by v. Kobell of the chlorite 
of Achmatoffsk, his analysis of the Schwarzenstein chlorite, Var- 
rentrapp’s analysis of the Achmatoffsk cholite, and v. Briiels of 
that from the Zilerthal. 
2. Chlorite-slate. .(Varrentrapp. ) 
16°39 : 5°66 : 18:84 ye ith lea 
16°39 ; 5-46 ; 1821 3(R)* Si+(R) Al. 
