No. 2385. CRYSTALLOCJRAPHW STUDY OF DATOLITfi—SEANKON. 519 



U (344) occurred on crystal 51 as a very narrow face, beveling the 

 edge between n (111) and Q (122), as shown in figure 17. The face 

 was bright but very narrow and gave a faint signal. The angles are: 



(344) Measured «p = 49° 24' p = 63° 18' 

 Calculated ^ = 49° 49' P = 63° 00' 



A = 0° 25' A = 0° 18' 



The same form was noted on two other crystals, but the faces were 

 entirely dull, yielding no signals. These were identified by their 

 zonal relations. 



S3 (345). A narrow line face, occurring with (343) and (344) on 

 crystal 51, gave a distinct signal, which, however, was so faint that 

 it could not be accurately measured. The form indicated by the 

 angles measured is (10.12.15). The position of the form, however, 

 shows the true indices to be (345), the discrepancy in the angles being 

 due to inexact measurement. The angles are given as follows: 



(345) Measured ^ = 52° 49' p = 59° 01' 

 (345) Calculated V " = 49° 50' p = 57°30' 



A= 2° 59' A = 1° 31' 



(10.12.15) Calculated^ = 52° 46' p = 59°08' 



A= 0° 03' A= 0° 07' 



The true indices of this form are thus somewhat in doubt. 



SB (382) occurred once as a very narrow and somewhat etched face, 

 beveling the angle between o (120) and m x (011) on crystal B8, as 

 shown in figure 12. The dim signal could not be accurately centered, 

 thus giving very inaccurate measurements, as shown below: 



(382) Measured <p = 30°38' p = 82°36' 



Calculated <? = 30° 37' p = 80° 21' 



A= 0° 01' A= 2° 15' 



X (455) occurred on crystal 14 as a narrow and somewhat etched 

 face between n (111) and ra x (011). The angles are: 



g) (6.15.2) is one of the forms which is of more or less doubtful 

 validity. It occurred on crystal 10 as a somewhat curved and etched 

 face between m x (011) and o (120), as shown in figure 19. The angles 

 are: 



(6.15.2) Measured <p = 33° 55' p = 84° 51' 



Calculated ^ = 32° 14' p = S4° 54' 



A= 1°41' A= 0° 03' 



