a . * 
: 2a | Scientific Inlelligence, 
fz 
‘PutocorirE, (or Rhombic Miéa) according to Meiseindelll apanipee 
variety of the brown, The optical character of these micas has been 
observed by the writer in connection with B. Silliman, Jr. , 
Biorrre (Hexagonal or Magnesia Mica) has the ratio 1: 1: 2, an nd 
Ghante RaSi+(zl, Fe) Si, which is essentially the formula of garnet. 
A chrome meguiene are gives the ratio 3 : 1 ; 2, but whether uniaxial 
or not is not certain. A Pargas biotite gives, 3 : 1: 2, and the formu- 
‘la R2 Si HBS: (Rammelsberg) ; anda Rosendal, 1: 1:25, or the for- 
mula 382 Si+28 
LEPIDOLITE or hits mica,.—The Lithia micas have been the subject 
of study by Rammelsberg, and he concludes that in them as we 
topaz, the fluorine replaces oxygen, or is in the same state of composi- 
tion as the oxygen. ‘There are several distinct chemical compou unis ° 
included, and it is not definitely known that they are all biaxial. 
Brewster observes that in one lithia mica part of the specimen was bi- 
axial and part uniaxial. The ratios given by Rammelsberg are, 
1:3: 6=R8i+# Si—mica of Ural, Chursdorf, Utd, Rozena, Altenberg (Stein). | 
a, 
&. 2:9: 15=2R Si+38 Si—mica of Zinnwald. 
c 1:2: 5=3R Sit 2% Si—mica of Juschakow 
d. 1:6: 7=R2 Si+6# Si—mica of Altenberg sent to Turner. 
In the Ural, grains Uté, and Rozena micas, the fluorine is to the 
Tagen as 1 : 20 ; the Altenberg, (Stein), 1:60; in the Zinnwald, 
1:14, orl: 11; in ie Juschakowa, 1:8; in the Altenberg, (Turner), 
The > Ural mica (Turner) affords then the formula,—writing for RSi 
+BEi, (R O+-Si 0?)-+-(R? 03-+Si 03), 
20[(R O+Si 03)+(R? 0%+Si O2)]+[(RF+Si F*)+(R? F2+SiF*)] 5 
and in the same way the other 8 ser be written out. Making 
O and F isomorphous, this formula becomes 
[R (0, F)+8i (0, F)>]4[R2(0, F)*+Si(0, F)>]. 
EMERYLITE and Euruytuire.—These species have Doe oy recent 
oon ey and the ee now stand as follow 
Emervuirte, J. Lawrence Smith. Corundellite ay Clingmanite, Sil- 
liman, Jr. =< oliated like 1 mica ; folia easily separable. Either in coarse 
plates or in masses consisting of aggregated — 
G.—2°995, Silliman, Jr. Lustre pearly. Color white. 
Translucent, to ane opaque. Folia brittle or nt set flexible. 
muscovite the protoxyds bear a small poeertos to the peroxyds, and the ratio is 
very near that derived fom some analyses of this species. The specimens look like 
a slightly altered mica, Including the a. the oxygen ratio is 159: 12: 15-01; 
he oxygen ratio for the second analysis is 4°16 : 15-24 6: 9°78, 
‘margarodite, excepting in the | : 
Lj Seem PP P ee eae Sivaiont } t; yet ther ly are di able 
“ phe the ratio 1: $: 1 and formula 3&3 Si+28 Si, which is the formula fer 
oe OR gy 
