82 
THE CONSTITUTION OF THE SILICATES. 
[BULL. 125. 
In apophyllite fluorine may partly replace hydroxyl, and K may 
replace the univalent CaOH. With K : OaOH : :1 :1 the composition 
of apophyllite becomes 
SiO» 52. 03 
CaO : 24.27 
K.0 6.79 
H 2 16.91 
100. 00 
The uncertain mineral plombierite may be a fourth member of this 
group, with the formula 
/Si,0 7 .CaH 3 
Ca< 
>Si 2 7 .Ca 2 + 9 aq. 
Ca< 
\Si 2 7 .CaH 3 
To the calcium-manganese silicate, inesite, various formula? are 
assignable. By Flink it is regarded as 2(0aMn)SiO 3 . H 2 0. But part 
of the water is stable at temperatures above 300°; and this fact is 
expressed by Schneider's formula (0aMn)Si 3 O 8 (MnOH) 2 . H 2 0. Both 
formula3 agree with the analyses approximately, but the latest analysis, 
that of Lundell,* is better represented by the following mixture: 
/Si 2 O 7 .0aH 3 /Si 2 7 .MuH 3 
Oa< Mn< 
>Si 2 7 .CaB -f 2H 2 0, and >Si 2 7 .Mn 2 +2H 2 
Oa< Mn< 
\Si 2 O 7 .0aH 3 \Si 2 7 .MnH 3 
which requires : 
Si On 
PbO 
MnO 
MgO 
CaO 
H 2 0. 
r ouiiu, 
Lundell. 
Calculated. 
42.92 
42.18 
.73 
1 
36.31 
37.44 
.37 
) 
8.68 
i 
9.84 
10.48 
10.54 
99.49 
100. 00 
With inesite another manganese silicate, bementite, is perhaps 
related, having the formula 
Mn< 
Mm 
Si 2 7 .MnH ; 
;Si 2 7 .Mn 2 
Si 2 7 .MnH 3 
See Hambere, Geol Foren. Forhandl., XVI, p. 325. 
