CLARKE.] 
TOURMALINE GROUP. 
61 
These formulae are uncertain, and need verification with material from 
other sources. At present they have only a reasonable probability. 
The tetrad silicate in them, however, will be seen to be highly prob- 
able when we come to the discussion of the other allied compounds 
in their proper connection later. 
There is one other borosilicate containing aluminum, axinite, whose 
relations are uncertain. Physically it differs widely from tourmaline, 
being triclinic, but on account of its composition it may fairly be con- 
sidered here. The analyses of it vary to a considerable extent, partly 
because of uncertainty in the determinations of water and boron, but 
also in other respects which indicate a mixture of molecules. Some 
analyses give orthosilicate ratios, provided that the boron is regarded 
as basic and equivalent to aluminum, but others show much too little 
oxygen. Boron, however, is essentially an acid-forming element, and 
it seems more probable that in axinite it has acid functions. The most 
typical axinite is that from Bonrg d'Oisans, and of this the best 
analysis is by Jannasch and Locke.* From this the following formula 
is easily derived : 
.B0 3 =A1-0H 
Al-Si0 4 EE, 
\si 3 G 8 ^ I °* 
in which the boron is regarded as part of an orthoborate molecule, 
derived from the acid H 3 B0 3 . 
This may be compared with Jannasch and Locke's analysis directly, 
and with the latter reduced by recalculating Fe 2 3 into A1 2 3 , the other 
bases all into their equivalents in OaO, and then bringing to 100 
per cent, thus : 
Si0 2 . 
B 2 3 . 
A1 2 3 
Fe 2 :i 
FeO . 
MnO 
CaO. 
MgO 
K 2 . 
Na 2 
H 2 . 
Found. 
Reduced. 
42.88 
6.02 
18.24 
.62 
7.10 
1.06 
19.89 
2.23 
.11 
.36 
2.14 
43.13 
6.06 
18.73 
29. 93 
2.15 
Calculated. 
43.32 
6.32 
18.41 
30.33 
1.62 
100. 65 
100. 00 
100. 00 
The formula may also be written 
.B0 3 =A10H 
Al-Si() 4 = ) ^ + 
-Si0 4 = ) 
lCa 3 
,B0 3 =A10F 
Al-Si 3 8 : 
X -Si 3 8 : 
Ca 3 
Zeitsch. Anorgan. Chem., VI, p. 57, 1894. 
