UNUSUAL TOURMALINE-ALBITE ROCK FROM ENOGGERA. 532 
relative proportions of soda, silica, and alumina shows that 
there is a considerable excess of the two latter. By using 
Harker’s or Osann’s tables we can easily calculate that the 
proportions of these three oxides in albite are very different 
from the ratios shown in the chemical analysis. 
Ratio in Albite. | NasO, | AlsO3. Si0s. 
| 
Actual .. iz as f is 8-57 | 24-99 63-40 
| | 
Calculated i es aya a 8-57 | 14-15 | 49-74 
i 
Excess .. we ey: he = 10-84 13-66 
It is difficult to explain this very large excess, even after 
the other bases have been allowed their quotas of silica and 
alumina. The presence of andalusite and quartz suggested 
itself, but search for these minerals proved fruitless. Possibly 
many of the minute inclusions observed in the albite may be 
quartz and andalusite, but these could not nearly account for 
the large excess of silica and alumina. The conclusion was 
forced on one that the silica and alumina were present in 
solution in the albite in spite of the fact that Foote and Bradley 
investigated this very problem and came to the conclusion 
that “no solid solution of quartz, corundum or nephelite in 
albite occurs which is greater than the apparent variation in 
composition due to the ordinary errors of analysis.’’? 
The excess of silica, anomalous though it seems, serves to 
explain in part another anomaly seen in the rock itself—viz., 
the absence of quartz in a tourmaline rock which (the structure 
suggests) has been formed by replacement. 
Turning now to the second analysis, we find it quite 
normal except in t e low percentage of water present. 
(V) DISCUSSION. 
(A) MINERALOGICAL. 
Mineralogically the rock, consisting as it does almost: 
entirely of tourmaline and albite, is almost unique. Only one 
7 Foote and Bradley, “‘ Constant Composition of Albite,” Am. Jour. 
Se., xxxvii, 1913, p. 47. 
