No. 2385. CRYSTALLOGRAPUIC STUDY OF DATOLITE— SHANNON. 521 



The agreement is good, and although observed only once, this is 

 considered a well-grounded form. 



I (T67) occurs on crystal 10 as a narrow face between i (T23) and 

 m x (Oil), as shown in figure 16. The face is partly dulled by etching 

 and yields a dim signal giving the following angles: 



(167) Measured ^ = 15° 22' p = 48° 18' 



Calculated <p - 14° 36' p = 48° 16' 



A= 0°46' A = 0°02' 



Although the values for A are small, the form was not confirmed 

 by measurement of any other crystals, and, since it does not fit in a 

 normal series as shown in the following discussion of zones, it must 

 be considered to be doubtful. 



m (1.6.12) occurred as a narrow line face, beveling the angle 

 between g (012) and p (T14) on crystal 55. The face, although 

 fairly conspicuous, was etched and rounded so as to yield only a 

 poor signal, which, owing to its dimness, could not be accurately 

 measured. The angles are: 



(T.6. 12) Measured ^=15° 14' p = 30° 06' 



Calculated ^ = 14° 30' p = 33° 11' 



A= 0°44' A = 3° 05' 



There is a marked probability that the indices have been incor- 

 rectly determined. 



o (T.6.14) occurred with the last as a distinct but rounded face, 

 beveling the angle between g (012) and k (115) on crystal 55. The 

 signal was dim and somewhat blurred. The angles are: 



(T.6.14) Measured <p=15°05' p = 27° 49/ 



Calculated ^=14° 28' p = 29° 16' 



A= 0° 37' A= 1°27' 



This form also must be regarded as requiring further confirmation. 



p (T.10.30) occurred as a dim face, beveling the angle between 

 t (013) and k (T15) adjacent to p (1.6.12) and p (T.6.14) on crystal 55. 

 Like these forms the face, though a relatively broad and prominent 

 line, is somewhat etched and rounded, although this is the best 

 established of the three forms, as shown by its angles, winch are as 

 follows : 



(T.10.30) Measured <p = 8° 06' p = 22°42' 



Calculated *> = 8° 38' p = 23° 05' 



A = 0° 32' A = 0°23' 



