Vol. 5] 



Louderhack. — Benitoite. 



355 



&(010) is always narrow and strongly striated vertically and 

 difficult to get readings on. Its position in the prism zone is 

 definite and its even truncation of the angle HOAllO leaves no 

 doubt as to its identity. 



As a constituent form of the crystals g is quite definite and 

 generally present, but its attitude is somewhat variable. It is 

 always more or less curved and generally dull. While in general 

 it lies in the zone of (111) and (311), it appears to be sometimes 

 curved in such a way that its traces with (111) and (311) are 

 not parallel, and in such cases the distance between these edges 

 is always greater along the edge g 3 /\g 4 and diminishes outwards 

 in both directions. "Where most simply developed it is a narrow 

 band and lies sensibly in the zones Tll-311, 221-221 and TT2-T10 

 corresponding to the symbol (211) ; but where more broadly 

 developed the lower portion approaches in attitude to (944). 



Measurements made on the poor reflections of the lower por- 

 tions of curved faces gave 



Measured. Calculated. 



<P p <P P 



(1) 52° 07' 52° 49' (944) =52° 28' 52° 58' 



(2) 51 17 51 31 (211) =47 29 50 5 



(3) 51 43 52 47 



Habit. By far the larger number of neptunite crystals are 

 attached at one end and grow out as comparatively slender prisms 

 six or eight times or even ten times as long as broad. A moderate 

 number show development of faces at both ends of the prism axis, 

 but the habit is always prismatic, and is somewhat similar to thai 

 described by Wallenstrom, but in the Greenland prismatic nep- 

 tunite the orthodome is the most important terminal form, and 

 occurs also in the first found prismatic type of the mineral 

 described by Nordenskiold. In the California neptunite as far as 

 known both ortho- and clino-domes are entirely lacking. 



The basal plane is always small and brilliant and in outline 

 commonly developed obliquely to the symmetry plane ; g is very 

 commonly dull and p frequently so; o 4 , Til is generally, .r. 111 

 frequently and i 4 , 112 sometimes striated parallel to the edges of 

 the diagonal zone 1 10-1T1-001-T12-T1 1-T10 ; <f\ Hi, r, 112, s\ 111 

 to edges of the corresponding zone, 110-001-lTO. The front pina- 

 eoid and the prism (110) are always present and the planeness 



