CONSTITUTION OF TOURMALINE. 
33 
with Li : Na approximately as 5 : 4. The slight deficiency in the alkalies 
is made up by the presence of small amounts of calcium, iron, and 
manganese, but the ratio Al 8 : Si 6 is very clear. The green tourmalines 
are all lower in alumina, and range downward toward the iron end of 
the series j and like the latter are representable as mixtures of the fol- 
lowing molecular types : 
BO :s (A10H) . Fe.II,. 
BOsCa . Fe 4 H,. 
BO :s LiH . Al 2 Li>H 4 . 
B0 3 NaH . ALNaH 2 . 
BO :i H, . ALNaH,. 
A. Al 5 (Si0 4 )o(B0 2 ) 2 
B. Al*(Si0 4 ) 6 (B0 2 ) 2 
C. Al r ,(Si0 4 ) 6 (B0 2 ).> 
D. Al.,(Si0 4 ) 6 (BO,), 
E. Al,(Si0 4 ),;(B0 2 ) 2 
Thus the dark, opaque green tourmaline from Rumford, Maine, is a 
molecular mixture corresponding to A 6 B 2 C 7 D U E 5 ; the similar mineral 
from Auburn is A 8 BiC 8 D 17 ; the light green from Auburn, A 2 CB : j l0 D 8 E,2, 
and the nearly colorless from Auburn, A1B5O20D10E35. From Brazil the 
dark green is A 3 Bi<J G D 8 , and the light green is AiB 2 9 D 8 E 5 . The com- 
plexity of these expressions is only apparent, not real, as a study of 
the original type formulas will show. They compare with the reduced 
analyses as follows : 
Kumford. 
Auburn, dark. 
Auburn, 
medium. 
Found. 
Calculated. 
Found. 
Calculated. 
Found. 
Calculated. 
Si0 2 
36.68 
10.26 
38.26 
6.78 
.34 
3.12 
.95 
3.61 
36.69 
10.69 
37.74 
6.90 
.34 
3.07 
.94 
3.63 
36.37 
9.98 
36.89 
7.94 
.17 
3.19 
1.06 
4.40 
36.45 
10.63 
37.21 
7.72 
.16 
3.14 
1.07 
3.62 
37.95 
10. 57 
38.11 
4.47 
.50 
2.58 
1.35 
4.47 
37.52 
. 10.94 
39.02 
4.28 
.50 
2.58 
1.35 
3.81 
B2O3 
A1 2 3 
FeO 
CaO 
NaO 
Li 2 
H 2 
100. 00 
100. 00 
100. 00 
100. 00 
100. 00 
100. 00 
Aubui 
n, pale. 
Brazil 
dark. 
Brazil 
light. 
Found. 
Calculated. 
Found. 
Calculated. 
Found. 
Calculated. 
Si0 3 
B,0 :i 
Al 2 :i 
FeO 
38.25 
10.30 
39.92 
2.75 
.43 
• 2. 55 
1.34 
4.46 
37,92 
11.05 
40.17 
2.56 
.49 
2.53 
1.34 
3.94 
37.24 
9.95 
38.66 
5.49 
.39 
2.90 
1.63 
3.74 
37.14 
10.83 
38.07 
5.24 
.35 
3.01 
1.64 
3.72 
37.49 
10.32 
39.86 
3.74 
.49 
2.59 
1.71 
• 3.80 
37.64 
10.97 
39. 04 
3.61 
.46 
2.76 
1. 69 
3.83 
CaO 
Na 2 
Li 2 
H 2 
100.00 
100. 00 
100. 00 
100. 00 
100. 00 
100. 00 
Bull. 167- 
