THE PHYSICAL CHEMISTRY OF THE CRYSTALLIZATION 
AND MAGMATIC DIFFERENTIATION 
OF IGNEOUS ROCKS | 
JH ks VOGr 
Trondhjem, Norway 
jut 
CaMgSi.O. (DIOPSIDE) AND SiO, 
The binary eutectic between CaMgSi,O,; (melting-point = 1391°) ~ | 
and SiO, (melting-point =ca. 1700°, see p. 330) consists, according 
to Bowen (Amer. Jour. Sci., Vol. XX XVIII [1914]) of 84 per cent 
Diops:16 per cent SiO., with melting-point =1362°, and at this 
temperature SiO, forms tridymite. 
THE TERNARY SYSTEM CaMgSi,0¢:Ab:An AND THE SEQUENCE OF 
CRYSTALLIZATION BETWEEN THE PYROXENE MINERALS 
AND PLAGIOCLASE 
The ternary system between the chemically pure substances 
CaMgSi,0¢, NaAlSi,O3, and CaAlL,Si,03 has recently been explained 
by N. L. Bowen in a treatise “The Crystallization of Haplobasaltic, 
Haplodioritic, and Related Magmas” (Amer. Jour. Sci., Vol. XL 
[x915]). 
The melting-points are: CaMgSi,Os, diopside=1391.5°. 
CaALSi,03, An=1550+2°. NaAlSi,0s, Ab=1100+ 10°. 
The binary eutectic Diops:An was determined as 58 per cent 
Diops:42 per cent An, with melting-point at 1270°. 
On account of the extremely high viscosity of the melting 
masses, consisting of predominant Ab, the binary eutectic between 
Diops and Ab could not be determined, but by extrapolation © 
(see Fig. 6) it lies at only a few per cent of Diops to nearly 
roo per cent Ab, and naturally at a temperature lower than the 
melting-point of Ab, consequently somewhat lower than 1100", 
thus a couple of hundred degrees lower than the eutectic between 
Diopsand An. From the theoretical explanation of Schreinemaker 
426 
