390 0. Andersen — Aventurine Feldspar. 



Table 7 



Ab 76 An 2 4 ; n = l - 545 



Form 



Measured 



Calculated 



from 



measurements 



Calculated 



from 

 axial ratios 



Measured 



Calculated 



from 

 axial ratios 



Pole : Normal to 001 ( p P and P ) 





46° 27' 



21° 17' 



20° 47' 



20° 44' 



58° 3' 





112 



49 58 



18 28 



20 48 



57 56 



58° 34' 





57 26 



13 13 



20 47 



58 19 







46 27 



23 9 



21 22 



. 21 42 



56 57 





112 



49 58 



21 7 



21 36 



57 6 



56 18 





57 26 



15 46 



21 36 



56 44 





Pole : Normal to 010 ( p M and M ) 



150 



150 



46 32 



17 10 











46 34 



16 40 



47 35 



16 







19 



31 



1 19 



34 



1 19 



28 



19 



22 



19 



25 



1 19 20 



19 30 



19 19 



63 



43 



63 



34 



63 



50 



63 



17 



63 



42 



63 



29 



63 33 



1 Direct measurement. 



Projections on (001) of the longer edges of lamellae after 

 (112) formed often + 72° with the a-axis. Lamellae after 

 (150) and (150) were oriented with the projections of the long 

 edges on (010), forming about —79° with the a-axis. 



Labradorite from Labrador.* 



The feldspar. — The cleavage pieces were fresh, of gray 

 color and showed a beautiful labradorization on cleavage faces 

 of (010). 



Extinction angle on (001) = 5*5° 

 " " " (010) = 16° 



/3 = 1-558 



* Specimens from the collection of the Geophysical Laboratory. 



