330 TE VOGE 
QUARTZ (QU) AND FELDSPARS. QU:OR, QU:AB, QU:AN, 
QU:AB-+AN, QU:OR:AB+AN 
The binary system Si0,:CaAl,Si,Og (An) has been examined 
by G. A. Rankin and Olaf Andersen’ (at the Geophysical Labora- 
tory, Washington) with the result: An, melting-point =1550°= 2°; 
Eutectic SiO,:An= 52 per cent An:48 per cent SiO., melting-point 
ag 322 
According to I. B. Ferguson and H. E. Merwin? (1918) the 
melting-point for tridymite is 1670+10°C; for cristobalite 
r7ro#10°C. K. Endell and R. Rieke* (1912) decided for cristoba- 
lite 1685+ 10°. N.L. Bowen‘ decided a somewhat lower tempera- 
ture, and C. N. Fenner’ thought he might fix the melting-point 
of cristobalite at 1625°, which, however, according to the latest 
precision-investigations, must be a little too low. 
It is a matter of course that Qu and Or, as well as Qu and Ab, 
in the same manner as Qu and An, must form a binary eutectic. 
Because of their extreme viscosity the binary eutectics Qu:Or 
and Qu: Ab are not experimentally determined. We may therefore 
here use the analytic method. 
We shall commence with graphic granite, the structure of which, 
as already established many years ago by W. C. Brégger,® is due 
to a simultaneous crystallization of quartz and feldspar. That is 
to say, the crystallization took place at a eutectic point or along 
a eutectic boundary curve. 
Referring to my earlier publications’ on the problem in question, 
we are going to give a collocation of all the hitherto published 
usable or at any rate somewhat usable analyses of graphic granite 
from pegmatitic granite dikes. 
t The System Anorthite-Forsterite-Silica,” Amer. Jour. Sci., Vol. XX XIX (1915). 
2 Amer. Jour. Sci., Vol. XLVI (1918). 
3 Zeitschr. f. anorg. Chemie, Vol. LX XIX (1913). 
4 Amer. Jour. Sci., Vol. XX XVIII (1914). 
5 [bid., Vol. XXXVI (10913). 
6 Geol. Foren. Forh., Vol. V (1881), and Zeitschr. f. Kryst. Min., Vol. XVI (2800), 
I, pp. 148-59. 
7 “Silikatschmelzlés.,” II (1904), and Tscherm. Mitt., Vol. XXV (1906). 
