CLARKE.] 
CONSTITUTION OF TOURMALINE. 
29 
sometimes replace the group B0 2 , an equivalency which is strongly 
indicated in the cappelenite group of minerals. 
The brown tourmaline from Gouverneur, New York, as analyzed by 
Kiggs, also reduces to a similar mixture of molecules, and its composi- 
tion may be written thus: 
5. Al 5 (Si0 4 ) 6 (B0 2 ) 2 . B() :! Ca . Mg 4 H 4 , 
3. Al 5 (Si0 4 ) 6 (B0 2 ) 2 . BO :! Mg . Mg 4 H 4 , 
2. Al 5 (Si0 4 ) 6 (B0 2 ) 2 . B0 3 NaH . Al 2 Na 2 H 4 ; 
and the comparison between analysis and theory is as follows;: 
Found . 
Reduced. 
Si0 2 
37.39 
37.54 
B 2 :! 
10.73 
10.76 
A1 2 S 
27. 79 
| 
28.72 
Fe 2 3 
.10 
TiO, 
1.19 
1 
FeO 
.64 
} 
MgO 
14.09 
14, 51 
CaO 
2.78 
2.79 
Na,0 
1.72 
} 
1.83 
K 2 
.16 
H 2 
3.83 
3.85 
100. 42 
100. 00 
Calculated. 
37. 32 
10.88 
28. 53 
14.52 
2.90 
1.93 
3.92 
100. 00 
By consolidating lime with magnesia the expressions for both tour- 
malines might be simplified; but in other cases this would not be 
warranted. In some tourmalines calcium seems rather to replace 
sodium, or else the group NaH, a probability which will appear later. 
In these two tourmalines the theoretical silicon-oxygen ratio Si, ; :i i 
is assumed, in accordance with my original formula. We may now 
consider the cases in which that ratio is exceeded, with more or less 
approach to the formula proposed by Penfield and Foote. This condi- 
tion is easily satisfied by regarding one of the component salts of tour- 
maline as slightly basic, containing the bivalent group =A1— O— H or 
=A1 — F as an essential factor. With this assumption, which recog- 
nizes the equivalency of hydroxy 1 and fluorine, the analyses reduce 
to the general type indicated in the two preceding examples. For 
instance, the white tourmaline from De Kalb, New York, has the follow- 
ing composition : 
10. Als(Si0 4 ) 6 (B0 2 ) 2 . BO :i (A10H) . Mg,H 4 . 
20. Al 5 (Si0 4 ) 6 (B0 2 ) 2 . B0 3 Ca . Mg 4 H 4 . 
3. Al5(Si0 4 ) 6 (B0 2 ) 2 . BO.Na, . Al ;! Na :i . 
For comparison the analyses by Penfield and Foote and by Kiggs are 
available. In this case the minute quantities of titanium are ignored. 
