556 



fenner: babingtonite from passaic county 



(Nat. Mus. No. 78,559) gave the same figure. Dispersion is 

 very noticeable. Pleochroism is remarkably strong. .In thin 

 sections a = dark green, /3 = claret, 7 = pale brown. Absorp- 

 tion formula a > jS = 7. Extinction angles up to 43° between 

 7 and the basal cleavage were observed. Vogt (quoted by Hintze) 

 gives an angle of 44° for the extinction-direction on sections 

 parallel with (Oil). 



Palache and Fraprie, in the article cited, give for the angle 

 between b and g, two prominent faces in the prism zone, 64°39'. 

 In the lozenge-shaped casts from New Jersey the faces are usually 



slightly irregular, but by making a large number of measure- 

 ments under the microscope, the average should give a close 

 approximation to the true value. Thirty-five measurements of 

 the acute angle were made, and the average was 64° 18'. 



