Am. Jour. Sci., Vol. V, 1898. 

 Zone inclined - 10 to A. 



Zone A, X (HO. 



/.one inclined in to a. 



« 4umiti «»- * 



Amies. --A1),, Vn, 



Lab. = Ab, An. 



Lab.=Ab s An. 



Anorthite=Ab n An.,, 



EXTINCTION OF TRICLINIC FELDSPARS IN AND NEAR THE ZONE 1 010. 

 Compiled from M. Michel-Levy's Etude sur la determination des Feldspaths, 1«R, Plates I-VII. 



The extinctions are referred to the trace of the twinning- plane and are represented by ordinates. The zero point of the zone answers to the 



The f S3 line g shows h the r extinction of an untwinned crystal, or of one lamella of an albite twin. The dotted line shows the extinction of an 



associated lamella rotated according to both the albite law and the < 'arlsbad lav 

 The stars (*) are placed on ordinates answering to most J r&iuent extuicttt 

 of these points. 



s, the abscissas corresponding nearly to the crystallographies position 



