190 



University of California. 



[Vol. 1. 



related in its optical properties to riebeckite, and sharply defined 

 from glaucophane, and in chemical composition lying between 

 riebeckite and glaucophane. It is very interesting to note that an 

 amphibole occupying just this position, so far as optical characters 

 are concerned, has been recently described by Dr. Whitman Cross* 

 as occurring in the form of a secondary growth on pyroxene in 

 an altered dyke rock in Custer Count}', Colorado. 



For convenience of comparison a table has been prepared show- 

 ing the properties of the Colorado and the California amphiboles, 

 and also of glaucophane and riebeckite: — 



Mineral. 



Pleochroism. 



Optical 

 Orientation. 



Opt. 

 Sign. 



Specif. 



Grav. 



Ratio of 

 Bases. 



Glaucophane. 



C = blue. 



b = reddish violet. 



11 = colorless to yellowish. 



b = b 

 r:c= 5° 

 behind. 





3-1 



Na : R : R 

 1:1:2 



Riebeckite. 



C = green. 



b = blue. 



H = deep blue. 



a>fi>c. 



b = b 



front. 



? 



>3-3 



2:2:1 



Blue amphi- 

 bole (Colorado). 



t = pale yellow. 



b = purple to violet. 



a =deep blue. 



> b>c. 



b = b 



front. 



? 



? 



r> 



Blue amphi- 

 bole (Berkeley). 



C = brown to greenish yellow. 

 b = reddish to bluish violet, 

 tl = deep blue. 



o>b>c. 



6 = b 



^:0 = i3° 

 front? 



? 



3-i6 



1:1:3 



A glance at the table shows the almost perfect identity of the 

 optical properties of the last two minerals, as well as their differ- 

 ences as compared with the others. In the absence of chemical 

 investigation of the Colorado amphibole, and, despite the totally 

 different paragenesis of the two minerals, their optical similarity 

 may be accepted as proof of their identity; and, as the present 

 investigation establishes it as a new species, it seems desirable to 



* Note on some Secondary Minerals of the Amphibole and Pyroxene Groups, 

 Amer. Jour. Sci., XXXIX, May, 1890. 



