CLARKE.] 
CONSTITUTION OF TOURMALINE. 
31 
Between the magnesium tourmalines and the iron tourmalines the 
closest analogy exists, and the identity of type is absolute. Taking, 
except when otherwise specified, the analyses by Iiiggs, all the iron 
tourmalines reduce to mixtures of the following isomorphous molecules: 
A. Al,(Si0 4 ) 6 (B0 2 ) 2 
B. Al 5 (Si0 4 ) 6 (B0 2 ) 3 
C. Al s (Si0 4 ) 6 (B0 2 ) 3 
D. Al5(Si0 4 ) 6 (BO*) 2 
E. Al6(Si0 4 )fi(B0. 2 ) 2 
B0 3 (A10H) . Fe 4 H 4 , 
B0 3 Ca . Fe 4 H,, 
BO :5 NaH . Al,NaH 2 , 
BO : ,NaH . Al 3 Na.,H, 
BO ;i NaH . Al,Na 3 . 
Molecules 0, D, and E are evidently identical, except in the varying 
replacements of sodium by hydrogen. A and B are similarly alike, so 
that actually only two fundamental compounds are assumed. From 
tbe commoner iron tourmalines lime is practically if not quite absent; 
and these may be interpreted very nearly as mixtures of A and 0, such 
as A 8 C 5 , A 7 5 , etc. If we take the minute quantities of lime into 
account, the black tourmalines from Brazil and from Stony Point, North 
Carolina, correspond to A n B 2 C 9 ; that from Auburn, Maine, to A3.5B2O.27, 
and that from Paris, Maine, to A 10 BiC 9 . It will be noticed that the 
molecule A is in excess of the other two, a condition which fits the 
analyses, but which is incompatible with the formula proposed by Pen- 
field and Foote. To satisfy the latter the number of A molecules 
should be exactly equal to B 4- C, giving the ratio Si 4 2 i or Si 6 3 i v 
The analyses in question are as follows: 
Brazil. 
Stony Point. 
Auburn. 
Paris. 
Si0 2 
B 2 s 
TiO- j 
34.63 
9.63 
35.56 
10.40 
.55 
33.38 
34.99 
9.63 
35.03 
9.02 
A1 2 3 1 - 
Fe 2 3 J 
FeO j 
32.70 
.31 
13.69 
.12 
2.13 
.33 
.08 
2.11 
.24 
3.49 
.06 
33. 96 
34. 44 
1.13 
12.10 
.08 
1.81 
.24 
.07 
2.03 
.25 
3.69 
8.49 
.04 
5.44 
.53 
trace 
2.16 
.24 
3.63 
14.23 
.06 
1.01 
.15 
Mnol 
MgO) 
CaO 
Li 2 ) 
Na,o| 
2.01 
.34 
3.62 
K 2 J 
H 2 0] 
f r 
] 
99.89 
99.52 
100. 42 
100. 00 
