0. Andersen — Aventurine Feldspar. 



383 



The hematite lamellae. — Large portions of the feldspar were 

 perfectly free from lamellae ; others contained many and showed 

 a strong aventurization. 



Most of the lamellae were elongated, often without regular 

 terminal edges. Sometimes they were also approximately six- 

 sided or rhomb-shaped. They were very small, seldom more 

 than 0-2 X 0-l mm . 



Orientation of the lamellae. — The goniometric measurements 

 are given in Table 3. The forms observed as planes of orienta- 

 tion were : (001), (010), (112), (112), (150), (150). Of these the 

 cleavage faces (001) and (010) contained very few lamellae, 

 often none. The majority of lamellae were orientated after 

 (112), fewer after (112), while (150) and (150) both contained 

 a considerable number. 



Projections of the elongated edges of lamellae after (112) 

 on (001) formed often about +73°, sometimes —14°, with the 

 a-axis. Other measurements did not seem to represent general 

 orientations. 



Table 3 



Ab 9 iAn 9 ; n — 1'535 



Form 



Measured 



Calculated 



from 



measurements 



Calculated 



from 

 axial ratios 



Measured 



Calculated 



from 

 axial ratios 







Pole : Normal to 001 ( p P and P ) 









47° 18' 



20° 26' 



20° 53' 



20° 40' 



58° 41' 





112 



58 45 



12 42 



21 2 



58 37 



58° 57' 





59 39 



11 36 



20 52 



58 55 







55 5 



17 57 



21 56 



21 48 



56 24 





112 



58 39 



15 12 



21 49 



55 49 



56 6 





59 55 



14 20 



21 58 



56 24 





Pole : Normal to 010 (p M and M ) 



150 



54 21 



10 54 



19 31 



19 24 



63 31 





150 



47 40 



15 12 



19 19 



19 17 



63 20 



63 27 



54 45 



9 49 



19 16 



63 58 



' 



Am. Jour. Sci. — Fourth Series, Vol. XL, No. 238. —October, 1915. 

 25 



