we” 
60 Scheerer on Isomorphism. 
(R) = 33:35 Mg, 0-42 Mn, 730 Ef (ammoniacal), 0-79 Al, 1-40 
Fe, 185 loss. . 
11. Monradite. | A. Erdmann. ) 
29-09 ; 15°39 
29-09 + 14:55 : (RY Sit. 
(R) = 31:36 Mg, 8: 56Fe, 4-048, 0: A excess. 
12. Talc. (Berthier.) 
(1) From Little St. Bernhard. 
30 2. 
A: 14-49 eyed: 
$043 16-06 ¢ 9 Sag 
gh From St. Foix 
28:88 : 13°59 R s Si 
28:88 : 14-44 (R)? Si*. 
In the former, (}) = 33°2Mg, 4-6 Fe, 3:53; in the latter, (R) 
197 Mg, 117 Fe, 81Ca, 26H. The tale from Si Foi aah 
tains moreover 1:7 Al. Deducting this as a 2 silicate, we obtain 
3 1 
the oxygen ratio = 27°69 : 13-59, also very nearly = 2; 1. 
13. Meerschaum.. | 
(1.) From Cabatias, according to Berthier, — 
215-14. 
(2.) From Gelloaeniasl according to the same, < (Ry Siz, 
28:05 : 15°22. 
(3.) From Morocco, <i to Damour, 
28:57: 14:2 
All the three oxygen na are more or less nearly = 2 : 1. 
Lychnell however has analyzed a meerschaum from the Levant, 
whose oxygen ratio is 31-62 : 14:11. Supposing this mineral not — 
to have been too highly dried, and to have been in a state of pu- 
rity, the formula Me Si+H must be adopted for it. Spadaite, 
picro 
smine, monradite, talc, and perhaps also meerschaum, have, 
as is seen above, one and the same chemical formula. The 
amount of water in the member (R) ranges between the limits — 
26 (talc) and 20 (meerschaum).  Picrosmine, monradite and tale 
occur crystallized, and all three of them in crystals belonging to 
ihe rhombic system.- In picrosmine the obtuse angles of the 
rhombic prism are very nearly 127°, in monradite 130°, and in 
talc 120°. The rhombie prism. of montadite and of picrosmine 
agrees also very nearly with the prism of serpentine, whereas that 
of talc is the same as that of villarsite. This accordance may 
cause some surprise, inasmuch as the formula for serpentine and 
villarsite is (R)* Si, whereas for the other three minerals the. for- 
mula is (R)? Si7. From analogous instances however, we are 
