abstracts: mineralogy 



523 



richer in silica, the melt is free from carbon dioxide. In each case the 

 compound containing more silica is the poorest in silica which can be 

 prepared pure at the particular temperature merety by putting to- 

 gether carbonate and silica. Moreover, rise of temperature, the pres- 

 sure remaining constant, favors the lower silicate. 



The study of systems of this type is important because their behavior 

 serves as a simple prototype of that of the magma, which is a highl}^ 

 complex system containing both volatile and non-volatile components. 

 The so-called " mineralizers" are merely volatile components; the effects 

 of their presence differ only in degree from that of the other components. 

 The main difference is due to the vastly greater effect of changes of 

 pressure and of temperature on the concentration (in the melt) of the 

 volatile component, by reason of the close relation of the concentra- 

 tion to that of the gas phase itself. In consequence of this, there is a 

 "mobility" of equilibrium which is characteristic of the magma and 

 without doubt very closely associated with many aspects of its behavior, 

 e.g., with the likelihood of eruption, differentiation, etc. P. N. 



MINERALOGY. — The melting phenomena of the plagioclase feldspars. 

 N. L. BowEN. Am. Jour. Sci. (4), 35: 577-599. 1913. 

 The method of quenching was applied to the determination of the 

 melting intervals of pure, artificial plagioclase feldspars. It was found 

 possible to determine accurately the temperatures of beginning of melt- 

 ing (solidus) for compositions ranging from pure An to Abs Aui and of 

 completion of melting (liquidus) for the range An-AbsAui. Very pure 

 natural material, Bakersville oligoclase was used to determine the point 

 on the solidus corresponding to its composition. Similar material, Amelia 

 County albite, served to fix the melting point of albite. The results of 

 this work are summarized below: 



COMPOSITION 



An 



AbiAns 



AbiAno 



AbiAni 



Ab2Ani 



Aba Aril 



Ab77-BAn22.6 



Ab4Ani 



AbgAni. . . . 

 Ab98An2 — 



TEMPERATURE OF BEGINNING 

 OF MELTING. SOLIDUS 



TEMPERATURE OF COMPLETION 

 OF MELTING. LIQUIDUS 



1550° ± 2° 



1521° ± 2° 



1490° ± 2° 



1450° ± 2° 



1394° ± 2° 



1362° ± 2° 



1334° ± 2° 

 1265° ± 3° 



