520 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.59. 



3 (766) occurred as a small face yielding a sharp signal on crystal 

 B 6. The angles are: 



(766) Measured <p = 61°45' p = 69° 12' 

 Calculated <p = 61° 29' p = 69° 20' 

 A = 0° 16' A- 0° 08' 

 The form, although it occurred only once as a measurable face, is 

 believed well established. 



fy (768) occurred once only as a small and somewhat etched face 

 on crystal B 9. Its angles are: 



(768) Measured <p = 61°24' p = 62°44' 

 Calculated <p = 61° 30' p = 63° 19' 

 A = 0°06' A = 0°35' 

 The order of agreement between the measured and calculated 

 angles is satisfactory, although the form needs confirmation. 



i (11.11.10) occurred as a narrow line face with 331 between 

 to (110) and n (111) n crystal B 6. While this might be considered 

 a form vicinal to n (111), the signals from the two faces are separated 

 by almost 2°, as shown below: 



(11.11.10) Measured ^ = 57° 44' p = 69°01' 



Calculated <p = 57° 38' p = 68° 58' 



A = 0° 06' A = 0° 03' 

 (111) Calculated ^ = 57° 38' p = 67°04' 

 A = 0° 06' A = 1° 57' 

 t (142) occurs as a well-defined face on crystal 41, as shown in 

 figure 18. Although small, this face gave an excellent signal, yielding 

 the angles: 



(T42) Measured <p = 21°22' p = 69°38' Crystal 41 



Calculated ^ = 21° 25' p = 69° 51' 

 A= 0° 03' A = 0° 13' 



The same form occurred also on crystal 10 as a narrow face with 

 (132) between b (010) and M (T22), as shown in figure 19. The 

 signal from this face, which was very narrow and etched, was too 

 dim to be accurately measured. The angles it gave are: 



(T42) Measured <p = 23° 25' p-68° 20' Crystal 10 



A= 2° 00' A= 1° 31' 



f (T43) occurred as a single face on crystal 41, as shown in figure 

 18. Although small, this face was bright and gave a good signal. 

 The angles are: 



(T43) Measured <p = 21° 51' p = 61°25' 



Calculated ^ = 21° 26' p = 61° 07' 



A= 0°25' A= 0° 18' 



