Robinson — Octahedrite and Brookite. 



183 



Figures 3a and 3b show the simplest type, the crystal being 

 terminated by the single pyramid s (322) in combination with a 

 small basal pinacoid. In figures 4$ and 46, s (322) is in combi- 

 nation with a dome y (104) and a much larger basal plane. 

 Figures 5a and 5b show the pyramids e (122) and z (112), which 

 are common on brookite, about equal in their development to 



s (322). The pyramid j3 (5'4'10) is new, occurring, as shown, as a 

 narrow face in a zone with e, z, and x. Of the domes, y (104) 

 and x (102) are common, while t (101) is new. In figures 6a 

 and 6h the general habit is more like that ordinarily observed 

 in brookite, the domes y, x, and t, and the pyramid e all 

 being common forms. The pyramid * (322), a (324), and 

 v (326) are in a zone and a (324) is new. The pyramid v (146) 

 is also new. In the prismatic zone a (100), m (110), and I (210) 

 are largely developed, while a (320) and k (410) are present as 

 narrow faces. 



All the crystals are of small size, ranging from 1*25 to 2*50 min 

 in width, 0*75 to l'75 mm in thickness, and 3 to 7 mm in length. 

 Their color is a dark reddish-brown and renders them too 

 opaque for optical examination in natural sections. Yertical 

 striations on the prismatic faces, with the exception of m, are 

 always very marked, giving them a dull luster. The terminal 

 faces are all somewhat striated, though not sufficiently to 

 greatly injure the quality of the larger ones. 



The faces observed, with their measurements as made on a 

 two-circle goniometer and their calculated values, are given in 



