386 



0. Andersen— Aventurine Feldspar. 



Orientation of the lamellm. — The goniometric measurements 

 are given in Table 5. The_planes of orientation were : (001), 

 (010), (112), (112), (150), (150), (110). 



Table 5 









Ab 8 oAn 20 ; n = 1*543 









Measured 



P 



d> 



Form 



i 



r 



Calculated 



from 



measurements 



Calculated 



from 

 axial ratios 



Measured 



Calculated 



from 

 axial ratios 







Pole : Normal to 001 ( p P and <p F ) 









59° 35' 



12" 14' 



20° 57' 



20° 43' 



57° 54' 





112 



61 17 



10 52 



20 50 



58 



58° 41' 









1 20 53 



58 8 





112 



60 39 



14 23 



21 50 



21 44 



56 36 



56 23 



61 20 



13 8 



21 34 



57 2 







Pole : Normal to 010 ( p M and M ) 







150 







1 19 30 



19 28 



63 33 



63 31 



150 







1 19 12 



19 18 



63 55 



1 Direct measurement. 



Lamellae after (110) were identified in sections after (001) 

 and (010) by the measurements : <£ P = 58° ; # M = 61°. 



Tbere were numerous lamellge after (112; and comparatively 

 few after (112). After (150) and (150) tbere were also many ; 

 after (001), (010), and (110) very few. 



For some of the lamellae after (112) the projections of the 

 longest edges on (001) were parallel to the a-axis. For other 

 lamellae in the same plane the edges formed +60° or +47° 

 with the a-axis. 



Oligoclase from Tvedestrand, Norway.* 



The occurrence at Tvedestrand has been described by Weibyf 

 as consisting of veins in gneiss, the essential minerals of the 

 veins being oligoclase (sunstone) and quartz ; accessory minerals, 

 apatite, hematite, cordierite, hornblende and zircon. 



* Specimens from the Mineralogical Museum of Kristiania University, 

 t Cited by Th. Scheerer, loc. cit., p. 154. 



