CLARKE.] 
META- AND DIMETAS1LICATES. 
89 
The formula R" 4 ( ArO) 8 (Si0 4 ) 2 (Si0 4 ) 2 would be exactly parallel with these, 
aud affords another expression for Tschennak's compound Al 2 RSiO G . 
On the ground of simplicity this is preferable to the more complex 
expression based on the formula of spodumene. 
The so-called " zircon pyroxenes, 7 ' rosenbuschite, wohlerite, laveuite, 
and hiortdahlite, I have already mentioned among the orthosilicates of 
zirconium. They can be given metasilicate ratios, following Brogger, 
by regarding the zirconium as present in the form of a metazirconate. 
If this explanation is correct, we should expect to find zirconates in 
nature, free from admixtures; but no such minerals are yet known. 
Artificial zirconates have, indeed, been prepared; but zirconium is 
more markedly basic than acid in its functions, and the analogy fur- 
nished by the orthosilicate, zircon, has been my guide in the interpre- 
tation of these species. Rosenbuschite, however, can be represented 
as a definite compound having structural analogies with the pyroxenes, 
as here formulated, with the composition 
Na TiF 2 Na 
I I! I 
SiO 4 _0a— SiO,— Ga— Si0 4 
F— Zrf )Zr— F 
\Si0 4 — Oa— Si0 4 — Ca— SiO/ 
II II II 
Ca Na 2 Ca 
which compares well with Cleve's analysis,* thus-. 
Found. 
Calculated. 
SiO 
31.36 
20.10 
6.85 
1.00 
.33 
1.39 
24.87 
9.93 
5.83 
30.30 
20.54 
6.73 
J 28. 29 
10.44 
6.40 
Zr0 2 
Ti0 2 
Fe.0 3 
La0 3 
MnO 
CaO 
Na>0 
F 
Less 
101. 66 
2.47 
102. 70 
2.70 
99.19 
100. 00 
This mode of interpreting the pyroxenes is so remote from our usual 
conceptions that I bring it forward with great diffidence. It unifies the 
group, however, it expresses the observed alterations of the several 
species, and despite its complexity it will be found to be sustained and 
strengthened by evidence brought out in the study of the amphiboles. 
This last-named group of highly important minerals resembles the 
pyroxenes in composition, and is explained by Tschermak in essentially 
the sante way. Their molecular weights, however, are taken as double 
*Zeit. Kryst. Min., XVI, p. 383. 
