1896.] NATURAL SCIENCES OF PHILADELPHIA. 211 



Molybdenite. Hexagonal, axis c:=1.908; 0001 A1011=65° 35' 

 Forms observed : c (0001, oP), o (1011, P, 0), p (2021, 2P, 2), 

 q (3031, 3P, 3\ m (lOlO, ooP, i). 



Angles : Observed. Calculated. 



cp= 77° 15' 77° 13' 



(77° 17') 

 (77° 7') 

 e(^=: 81° 31' 81° 23' 



mm= 60° 2' 60° 



Besides these, the angle c m was observed as 89° 48' and several 

 other angles near 90° on different crystals, but in general the images 

 from m in this zone were imperfect. The angle c o=65° 35' was 

 obtained in the same crystal in adjacent zones, it was observed on 

 several crystals. Oscillatory combination and probably vicinal 

 planes render the measurements ^somewhat irregular but the above 

 shows that the crystals may be explained on a hexagonal basis. 

 The angle commonly observed is cp^=n° 13' and has been reported 

 as 75°. This seems to show that the pyramid 2P, (2021) is more 

 common than the others. Many crystals only show two pyramids 

 and the basal pinacoid, in others the prism is more prominent. 

 While it is still possible that better crystals may show the mineral 

 to be monoclinic, the above results are of sufficient value to place 

 on record. It may be added that etching figures on the basal 

 cleavage seem to indicate a hexagonal, perhaps rhombohedral 

 crystallization. 



