THE MINERALOGRAPHY OF THE FELDSPARS 

 PART IP 



HAROLD L. ALLING 



University of Rochester, Rochester, New York 



Introduction 



The Potash-Soda Series 



The Diagram of Vogt and Warren 



The Diagram of Dittler 



Combination of the Two Extremes 



The Diagram of Makinen 



Thermal Studies 



Dimorphism 



Orthoclase vs. Microcline 



Albite and "Barbierite" 



Thermal Diagrams and Dimorphism 



X-Ray Analysis 

 The Soda-Lime Series 

 The Potash-Lime Series 

 The Zoning of Feldspars 

 The Twinning of Feldspars 

 Potash-Soda-Lime Feldspars 



Specific Gravities 



Indices of Refraction 



Extinction Angles 

 Sunstone and Aventurine Feldspars 

 Barium Feldspars 

 Strontium Feldspars 

 Conclusions 

 Acknowledgments 



INTRODUCTION 



Part I of this study of the feldspars^ is an attempt to summarize 

 our knowledge of the physical-chemistry of this group of minerals. 

 The method of attack is that of the phase rule. 



' Contribution from the Department of Geology, University of Rochester, 

 Rochester, New York. 



^^H. L. Ailing, Jour. GeoL, XXIX (No. 3, 1921), 193-294. 



282 



