EQUILIBRIUI\I RELATIONS AND FACTORS INFLUEXCIXG T H E I R DETERJIIXATIOX I X T H E SYSTEM Ii2SiO~-Si02 F. C. KRACEK, S . L. BOWES,
AND
G. W. MOREY
Geophysical Laboratory, Carnegie Institution of Washington, Washington, D . C. Receiced June 15, 1957
In an earlier paper (2) the equilibrium relations at the liquidus, and to some extent those among the crystal phases occurring in this system, were described. Further work in this Laboratory disclosed that the liquidus relations for the disilicate KzSi205required modification for reasons which will be discussed below, and accordingly the opportunity was taken to work over the entire system. The new results are presented particularly from the point of view of emphasizing the factors which influence the attainment of equilibrium. EXPERIMENTAL METHODS FOR THE LIQUIDTX
The methods of study remained the same as before, the liquidus being determined in all cases by the method of quenching. For details we refer to the earlier paper. -111 the mixtures studied were freshly prepared, crystallized dry, and the liquidus was determined on the crystallized material at once to avoid the disturbing effects produced by the absorption of moisture. For this reason we also have avoided the use of hydrothermal methods of crystallization used formerly to de\-elop IiZSi409 and quartz crystals in the appropriate region of the system. The tetrasilicate, K2Si409, v a s found to crystallize in the dry way with some reluctance a t 680°C. to 700"C., the most advantageous procedure being alternate heating and crushing to distribute the nuclei formed throughout the mass of the preparation. Usually three crushings with intermediate heatings of about tn-o hours' duration sufficed to produce an abundance of sinal1 4
