0. Andersen — Aventitrine Feldspar. 



391 



Composition : Ab 49 An 61 , a labradorite very near andesine. 



The cleavage pieces were twinned with coarse lamellae after 

 the albite law. 



The hematite lamellm. — There were but few reflecting 

 lamellae and the aventurization was accordingly very indistinct. 

 Most of the lamellae were opaque, but some were transparent 

 with the characteristic colors of hematite. They were often 

 linear, but sometimes approximately six-sided or irregularly 

 rounded. The largest measured - 03 mm in diameter. 



Orientation of the lamellae. — The goniometric measurements 

 are given in Table 8. The planes of orientation were : (112), 

 (112), (150), (150) each with about the same number of 

 lamellae. The linear, strip-shaped lamellae after (112) and 

 (112) were generally oriented with the projections of the long 

 edges on (001) parallel to the a-axis. The long edges of 

 lamellae after (150) and (150) were frequently parallel to the 

 <?-axis. 



Table 8 



Ab 4 9An 5l ; n = 1'558 



Form 



150 



150 



Measured 



Calculated Calculated 



from from 



measurements axial ratios 



Measured 



Calculated 



from 

 axial ratios 







Pole 



: NoTmal to 001 (p P and <p P ) 





112 



57° 20' 



14° 12' 



20° 53' 



20° 51' 



57° 53' 



57° 58' 



112 



57 14 



16 24 



21 33 



21 34 



57 23 



57 10 







Pole 



: Normal to 010 ( p M and <j> u ) 





55 30 



11 32 



57 39 



10 37 



54 49 



9 7 



55 48 



8 23 



19 39 



19 48 



18 44 



19 39 



19 23 



18 48 



63 



54 



64 



4 



63 



46 



fc3 



55 



63 43 



It should be noticed that the plane of labradorization on 

 (010) does not coincide with any of the planes of orientation 

 of the aventurizing lamellae. 



Microcline Perthite from Perth, Ontario, Canada.* 



The feldspar. — The aventurine feldspar from Perth was 

 described by Des Cloizeauxf as an orthoclase perthite. The 



* Specimens from U. S. National Museum ; Lea collection, No. missing, 

 t Ann. Chim. Phys. (5), ix, 465, 1875. 



