Scheerer on Isomorphism. 63 
This chlorite slate was from the Pfitschthal. The composi- 
tion of chlorite bears therefore a very simple relation to that of 
chlorite slate. 4; 
: 3. Ripidolite. 
1.) From Rauris, according to v. Kobell : 
13-54 : 8°63 : 16-04. 
(2.) From St. Gothardt, according to Varrentrapp : 
3°18 : : 15°81, 
(3.) From the Zillerthal, according to v. Kobell: 
1419 : 9-70 : 16°76. 
Mean of the three analyses : 
13°67 ; 8-99 : 16°20 Sse ee age 
13-50 : 9-00 : 16°50 t 3(R)° Si-+2(R) Al. 
28 4. Pennine. (Schweitzer.) 
«17-38 : 4-44; 18:80 lal pte 
1738: 4:35: 1883,¢ &(R)° Si+-(R) Al. 
The oxygen ratio is calculated from the mean of two experi- » 
ments. 
5. Xanthophyllite. (Meitzendorff. ) 
8°47 ; 20:53 ; 13-20 Tegner 
8-80 : 19-80 : 13-20 i A(R)? Si-+3(R)? Al’. 
_ From the mean of four analyses. 
6. Leuchtenbergite. (Komonen. ) 
17°78 : 8:38 : 16°74 i ee 
17-00 : 8:50 : 15-60 ; A(R)" Si+(R)* ae. 
It is here assumed, in accordance indeed with Komonen, that 
this mineral contains no protoxyd of iron, but 3°33 per cent. of 
the peroxyd. Leuchtenbergite is of a pale yellow, almost, in- 
deed, colorless, and can therefore scarcely be supposed to contain 
enough of the protoxyd to correspond with 3-33 Fe. It is 
possible that: the oxygen ratio may be 17:0 : 8:5: 17, and this 
would agree more closely with the ratio obtained from anal- 
ysis than what is given above. But in that case the formula 
would be, a(R)? Si+(R)? Al, which does not, it is true, appear - 
probable, inasmuch as the silica and the alumina are therein 
combined with equal quantities of base. It may be further sup- 
posed that the base in combination with the silica consists only 
of magnesia (with a certain quantity of lime), while that combin- 
ed with the alumina is composed of magnesia and water. The 
mineral, it is to be observed, contains 35°36 Mg, 1:75 Ca, 8:68. 
The formula would then become modified as follows, 
. 2 Mg? Si+(R)? Al. 
_ Cases analogous thereto have been already adduced, and there 
is another similar instance in the composition of the next mineral. 
sil 
