412 



MINERALOGY 



trie layers. Since it is triclinic, extinction is always at an angle, 

 and when measured on the basal cleavage in regard to the brachy 



FIG. 461. Albite from Pfitsch, Tyrol. 



cleavage cracks it is 5 ; when measured on the brachy cleavage in 

 reference to the basal cleavage cracks it is 19. The interference 

 color is a little higher than orthoclase, but still gray of the first order. 

 The axial plane is nearly perpendicular to 010. The acute bisec- 



FIG. 462. Polysynthetic Twinning in Albite, Crossed Nicols. 



