FENNER, THE WATCHUNG BASALT 117 



NaoOAloOgGSiOoeHgO. In heulandite we have similar relations, but 

 with SHoO. Typical analcite is Na20Al„034Si022H20, but a small 

 amount of lime usually enters. Similarly, natrolite is iSTaaOAljOgSSiOj- 

 2H2O, with a little lime sometimes present. 



"With most of the species, a little potash is frequently present and 

 doubtless would be found by analysis in the Watchung minerals, but no 

 distinctively potash zeolite has been noted. 



From the manner in which the ratios of the molecules vary in the same 

 mineral, it appears necessary to consider the form of union in the zeolites 

 to be that of solid solutions rather than that which is usually termed 

 chemical combination. 



Each of the species enumerated may be considered a separate and 

 distinct chemical phase. Including prehnite, pectolite and quartz, the 

 phases present are as follows: 



1. Labradorite and albite, 7. Heulandite, 



2. Quartz, 8. Stilbite, 



3. Prehnite, 9. Natrolite, 



4. Pectolite, 10. Scolecite, 



5. Analcite, 11. Laumontite. 



6. Chabazite, 



The phase rule states the number of phases which may be present in a 

 system in equilibrium under given conditions of temperature, pressure 

 and concentration.^^ 



In the fundamental equation P = C -(- 2 — F, 



P = number of phases, 



C = number of components, 



F = degrees of freedom (i. e., the numerical value of the variables, 

 temperature, pressure and concentration). 



In the system which we are considering, the components are five in 

 number as follows : NagO, CaO, AI2O3, Si02, HgO. 



With regard to the numerical value which should be ascribed to F, 

 some consideration is necessary. Temperature is without doubt in this 

 case an independent variable. Pressure should be considered as depend- 

 ent upon temperature, for in those portions of the system in which it was 

 somewhat independent of temperature, no gaseous phase was present. 

 Concentration probably varied from an independent function in the 

 earlier stages to a dependent function in the later on account of the dis- 

 turbing feature introduced by the presence of boric acid. After this had 



^ Alexander Fixdlat : Op. cit., p. 16. 

 W. D. Baxcroft : "The Phase Rule," Ithaca, N. T., pp. 1-5, 1897. 



