177 
being known as Margarodite. 
ROSIO, + 2(R,0,Si0,) + kHO 
: 
, 
«‘ The Micas of the Dublin, Wicklow, and Carlow granites, 
analyzed by me, belong to the Margarodite genus, and contain 
two atoms of water, corresponding to k = 2. 
“The following are the analyses of three micas selected 
from three distant localities of the granite chain of the south. 
east of Ireland. 
Silica, . . . 43°47 
Alumina, . . 3142 
Peroxide ofiron, 4°79 
fiime, -. . ..- 138 
Magnesia, . . 1°13 
Potash, . . . 1071 
Boge, . . . . see 
Loss by ignition, 5°43 
. 99°77 
Meuica, . . . 44°71 
Alumina, .. 31°13 
_ Peroxideofiron, 4°69 
Lime, ... 1:09 
Magnesia, . . 0:90 
Berotash,. . . 9°91 
memogs,. . . . 1°27 
_ Loss by ignition, 6-22 
99°92 
q gray, transparent. 
Atomic Quotients. 
0959 . . . 2°863 
0611 
0:059 
0:049) 
0:056 | 
0:228 
0:046 
0603. . . 1:800 
} 0670 2000 
Atomic Quotients. 
0987 . . . 2973 
0:606 
‘ 4 * 
pose | 0064 21000 
0-035 
0.045 
211 [0832 1-000 
0-041 J 
0691 . . . 2083 
a 1131 e 
«6 No. 1. Mica from the Three-Rock Mountain, county 
of Dublin; gray, transparent, containing specks or flakes of 
‘a bronze-coloured or black mica. 
Per Cent. 
no ww 
_ 
a “ No. 2. Mica from Glendalough valley, county of Wick- 
_ low, gray, transparent, with specific gravity = 2-793. 
Per Cent. 
* No. 3. Mica from Mount Leinster, county of Carlow, 
