PALACHE AND FRAPRIE. — BABINGTONITE. 887 



Dauber's elements were based on a very large number of measure- 

 ments on crystals of babingtonite from Arendal. His values for many 

 angles show a considerable range, up to a degree or more, on either side 

 of the mean value. Our measurements of interfacial angles, as shown 

 in Table I, show a like range, and the means agree on the whole so closely 

 with Dauber's calculated values that it was deemed best not to attempt 

 to establish new elements for the Somerville mineral. Moreover the 

 co-ordinate angles calculated from them for the two-circle readings agree 

 closely with the measured angles, as may be seen in Table II. 



The forms may be characterized as follows. 



In the prism zone a (100) and b (010) are always present, generally 

 brilliant and free from striations, but often slightly curved. 



h (110) is generally present as a very narrow, brilliant face. 



g (210) and f (320) are generally both present, most often in oscil- 

 latory combination as a broad, gently curved surface striated vertically — 

 a very characteristic feature of crystals from this locality. When f is 

 absent g is less deeply striated, but is rarely perfectly plan.e. Notwith- 

 standing their striation, both faces give good reflections. 



k (110). A number of faint reflections were observed in the vicinity 

 of the faces f and g, but the only one which was observed more than 

 once and was assignable to a definite form was the new form k, which 

 was found with both faces on one crystal and a single face on another. 

 The faces were narrow and reflection poor, but the form seems assured. 



c (001) is always present, generally plane, but sometimes faintly 

 striated parallel to intersection with s and o, or faceted. 



The domes o (Oil), s (Oil), and d (101) are always bright faces 

 giving good images. They are all three present on many crystals, s is 

 never lacking, and d is more frequently absent than o. They vary much 



is unsatisfactory in not making the dominant and most easily recognized zone the 



Dauber. Dana. Goldschmidt. 



n (101) (221) (Oil) 



u (054) (010) (640) 



V (035) (410) (350) 



w (025) (730) (250) 



X (305) (10. m 3) (053) 



y (205) (551) (062) 



p(lll) (401) (111) 



t(112) (6^1) (121) 



i (n2) (1261) (121) 



