64 
THE CONSTITUTION OF THE SILICATES. 
[BULL. 125. 
This formula, in contrast with that of Penfield and Pratt, and with 
their reduced analysis of staurolite from Lisbon, ^N. H., gives the sub- 
joined percentage composition : 
Lisbon. 
P. and P. 
New 
formula. 
SiO^ 
27.44 
55.16 
15.72 
1.68 
26.32 
55.92 
15.79 
1.97 
27.90 
55.35 
16.75 
Al 2 Oi 
FeO 
H.O 
100.00 
100. 00 
100. 00 
If, now, we assume that the actual staurolite is slightly altered by 
hydration, some Fe being replaced by H 2 and by FeOH+H, the dis- 
crepancies between formula and analyses are sufficiently accounted for. 
The new formula is more symmetrical than the old one; it better 
expresses the alterability of staurolite into muscovite, and it seems to 
satisfy the evidence with sufficient completeness. When we remember 
that staurolite is excessively liable to inclusions and alterations, a very 
sharp agreement between analysis and theory is not to be expected. 
Still another orthorhombic species, harstigite, has a formula anal- 
ogous in some ways to that of staurolite. For harstigite there is but one 
analysis extant, which gives, nearly 
SiO 4 ^0aH 
Al-SiO 4 =0aH 
\si0 4 =Mn 
I 
Oa 
.Si0 4 =Mn 
M-Si0 4 =CaH 
^SiO.^CaH 
This, in comparison with Flink's analysis, gives 
SiO, . 
A1 2 0, 
MnO 
Mg() 
CaO. 
K 2 . 
Na.0 
H 2 0. 
Found. Calculated. 
38.94 
39.13 
10.61 
11.09 
12.81 • 
\ 
15.43 
3.27 
29.23 
) 
30.44 
.35 
> 
.71 
s 
3.97 
3.91 
99.89 
100. 00 
a result which is fairly satisfactory, 
are evidently needed. 
More data relative to harstigite 
