Andersen — System Anortldte- Forsterite- Silica. 407 



Art. XXYII. — The System Anorthite-Forsterite-Silica ; 

 by Olaf Andersen. 



Contents. 

 Introduction. 

 I. Experimental "Work. 



Preparation of mixtures. 

 Thermal study. 



Heating curves. 

 Quenchings. 

 II. Description of Solid Phases. 

 Anorthite. 

 Forsterite. 



Cristobalite and Tridymite. 

 Clinoenstatite 

 Spinel. 



III. The Binary Systems. 



The system forsterite-silica. 

 The system anorthite-silica. 

 The system forsterite-anorthite. 



IV. Discussion of some Types of Ternary Systems without 



Solid Solution. 

 General remarks. 

 Type 1. 



Synopsis of terms. 



Crystallization curves. 



Phase relations. 

 Type 2. 

 Type 3. 



General qualities of curves and points. 



Examples of crystallization. 

 Type 4. 



Qualities of boundary curve jo. 

 Type 5. 



Recurrent crystallization of a solid phase. 

 V. The Anorthite-Forsterite-Silica System. 

 The spinel field. 



Mixtures with excess of MgO. 

 The ternary field. 



The alteration point. 



The ternary eutectic. 



The boundary curves. 



The isotherms. 

 Normal crystallization in different sections of the ternary field. 



The eutectic field. 



The reaction field. 



The section anorthite-clinoenstatite. 

 Crystallization with removal of forsterite from the liquid. 

 VI. Some Applications of the Results to Petrologic Problems. 

 General remarks. 

 Application of the reaction principle to olivine-bearing rocks. 



Magmatic resorption of olivine. 



Summary of application to olivine-bearing rocks. 

 Remarks on spinel-bearing rocks. 

 Summary. 



Am. Jour. Sci.— Fourth Series, Vol. XXXIX, No. 232.— April, 1915. 



27 



