J¥. L. Bowen — The Ternary System, etc. 207 



Art. XIX. — The Ternary System: Diopside — Forsterite — 

 Silica ; by N. L. Bowen. 



Contents : 

 Introduction 

 Method of Working 

 The Binary Systems 



The System Mg a Si0 4 -SiO a 

 The System CaMgSi 2 6 -Si0 2 



Lime-Magnesian Amphibole 

 The System CaMgSi 2 6 -Mg 2 Si0 4 

 The Ternary System 



Preliminary Statement 

 General Character of the Fusion Surfaces 

 Melting-point of Cristobalite 

 General Character of the Boundary Curves 



Brief Theoretical Discussion of Solid Solution in Ternary Systems 

 Methods of Determination of the Three-Phase-Boundaries 

 The Composition Method 

 The Temperature Method 

 The Course of Crystallization in Typical Mixtures 



Crystallization with Perfect Equilibrium between Liquid and 



Solid Phases 

 Precipitation, Complete Solution and Re-precipitation of 



Forsterite 

 Crystallization without Interaction between the Liquid and 

 the Solid Phases already Separated 

 Importance of Distinguishing between the Two Types of Crystal- 

 lization 

 The Pyroxenes, Diopside-Clino-enstatite 

 Comparison of the Present Eesults with Earlier Work 

 Summary of Comparison of Results 

 Optical Study 

 Forsterite 



Cristobalite and Tridymite 



The Diopside-Clino-enstatite Series of Pyroxenes 

 Twinning 

 Extinction Angle 

 Refractive Indices 

 Optic Axial Angle 



Summary of Optical Properties of the Pyroxene Series 

 Natural Pyroxenes with Analogous Optical Relations 

 The Eelation of Clino-enstatite to Enstatite 

 Bearing of the Eesults on Petrologic Problems 

 The Series of Lime-Magnesia Pyroxenes 

 Eesorbed Olivines in Natural Eocks 

 Eecurrent Crystallization 

 The Significance of Zoned Crystals 

 Consequences of the Possible Sinking of Early Crystals in a 



Fluid Magma 

 Dissociation in the Liquid Phase and its Eelation to Crystallization 

 Freezing-point Lowering in Silicate Mixtures 

 General Summary 



Introduction. 



The system dealt with in the present paper is a part of the 

 more general ternary system CaO-MgO-Si0 2 , and is that part 

 which is probably of greatest interest to the petrologist, since, 



