662 /. E. L. VOGT 



ourselves with the pneumatolytic, pyrohydatogen, and hydrotermal 

 processes effected by the escaping gas. 



During the crystallization of the magma the light volatile 

 compounds will conduct themselves in different ways: 



1 . Some will, if the gas pressure is sufficiently high, escape from 

 the magma. 



2. Some will be inclosed in the crystallizing minerals as gas- or 

 liquid-inclusions (for instance, the well-known pores in quartz, at 

 low temperature chiefly consisting of liquid CO2). 



3. Some may enter in solid solution into the crystallizing miner- 

 als. The quantity calculated by weight — or m.olecular weight — • 

 of these "occluded" gases is, however, very little.^ 



4. Some may, under certain circumstances, enter into the crys- 

 tallizing minerals, for instance H2O in muscovite, biotite or horn- 

 blende, CO2 in calcspar, etc. 



5. The rest of the gas will remain in dissolved condition in the 

 magma and be concentrated in the mother-liquid, by continuously 

 decreasing temperature until it reaches Q. 



These light volatile compounds dissolved in the magma exist 

 in the reciprocal solution in the same manner as the other solution- 

 components. If we think of a magma containing mix-crystal 

 components, as Ab and An besides dissolved water, the water will 

 not influence the mix-crystal system. And if we have a ternary 

 system of two components independent of each other, a and b 

 and also a little water (in lesser amount than that equivalent to Q 

 on Figs. 52-53), the sequence of the crystallization will be between 

 a and b, dependent on the quantitative relation between a and b 

 in relation to a eutectic boundary curve, beginning at the binary 

 eutectic Ea-b- The further extension of the curve will be stipu- 

 lated by the third component, H2O, present in small amount. With 

 a slight quantity of H2O the relation between a and b on the bound- 

 ary curve will be almost exactly the same as in the binary eutectic 

 Ea_b. That is to say, the sequence of the crystallization between 



' By heating to below the melting point of the rocks these occluded gases may- 

 escape and thereby break the rock into pieces. In this manner many rocks (granite, 

 syenite, gabbro, etc.) may be completely desintegrated by fire. 



