W. T. Schaller and F. L. Ransome — Bismite. 175 



Doubtful forms : 

 (0001) : (2025), 



Meas. 



15° 



16 r 



14 c 



18 



Calc. 



56' 

 26 



" : (1012), 16 u -20 v 



The value for the c axis was obtained from three measure- 

 ments that were considered as the most accurate. The others 

 gave values agreeing fairly well with the one adopted, as is 

 shown below. The crystals were measured on the two-circle 

 goniometer and the p angle for these forms is the angle 

 between that form and the base. 



The three best measurements are : 



p 



{10151 



= 



I 



33' 



Po 



= 



•6627 



cryst. 



No. 



1 



p 



{1015} 



=z 



7 



36 



a 



= 



•6672 



a 



a 



4 



p 



;ioi4| 



=z 



9 



31 



ic 



= 



•6706 



it 



a 



2 



Av. p o = -6668 ; c = 0-5775. 



An average of the other measurements gave values closely 

 agreeing. Thus : 



p 



(1016} 



= 6° 37' 



p o — -6960 



. cryst. 



No. 



3 





u 



= 6 41 



"° = -7031 



a 



a 



6 



p 



{10141 



=: 9 31 



" — -6706 



a 



u 



6 



p 



{1013} 



— 12 11 



" = -6477 



a 



a 



6 





u 



= 12 26 



" = '6614 



u 



u 



4 





u 



= 13 18 



" = -7102 



a 



u 



1 



Av. 



•6815 



The following measurements of faces giving no distinct 

 reflections also showed close agreement : 



P {1013; 



= 12°-14° (av. 



13°) 



Po = 



•69 



cryst. 



No. 



1 



P {2025; 



= 15° 







•67 



u 



a 



2 



p {1012! 



= 16°-20° (av. 



18°) 



a 



•65 



it 



a 



1 



p i 01 * 1 } 



^ 35 c 





a 



•70 



a 



a 



5 



a 



= 32^° 





a 



•64 



a 



a 



6 



P {2021} 



= 54 5 





a. 



•69 



a 



u 



1 



a 



= 54° 





u 



•69 



u 



a 



6 



The values for p just given show that the interpretation of 

 the forms is the correct one. 



Of the six crystals (all incomplete) that were measured, only 

 two need to be briefly described. 



Fig. la is an orthographic projection of a crystal (No. 1), 

 showing the trigonal distribution of the rhombohedra, and the 

 triangular markings on the base, 



Fig. \h shows a similar projection of cryst. No. 6, with a 

 negative rhombohedron. 



