Robinson — Ootahedrite and Broohite. 



181 



plex combination is represented with two additional faces, o 

 (107) and v (117). These two figures show all the prominent 

 forms as well as their relative development. 



The complete list of faces observed is as follows : 



c (001) o (107) y (902) v (1-1-28) 



e(101) tf(301) p (111) p (1-1-40) 



x (103) w y (5-0-19) villi) 



The errors in the measured values of the above faces as com- 

 pared with the values given by Dana* range from V to 10', 

 the average being 3J-'. Though most of the faces give rather 

 poor reflections, the measurements are all close enough to 

 clearly establish their identity. 



\(a). 



Z(a) 



(b) 



The form v (1-1-28) was first observed by Seligmann,f who 

 identified it with but moderate certainty, owing to the poor 

 development of the faces on the crystals examined by him. 

 The angles measured on two of these crystals leave no doubt as 

 to the correctness of the indices established by him, as is shown 

 by the following : 



Calculated. Measured (I). Average. 

 5° 7f 5° 3' 



5 12 5° 7f 



5 8 



Measured (II). Average. 

 5° 10' 5° 11' 



5 12 



The above measurements and the fact that the face lies in 

 the zone c^p are sufficient to establish the identity of this 



* System of Mineralogy, 6th ed., 1892, 240. 

 f Zs. Kr., ii, 337, 1886. 



