426 R. W. Richards — New Habit for Chalcopyrite. 



In Hintze's Handbuch der Mineral ogie, sixteen cases are 

 noted of the occurrence of the form e, and only seven of m. 

 With the exception of one or two cases, either one or the other 

 or both forms are subordinate. The Somerville crystal seems 

 novel in showing these forms predominant and, perhaps, except- 

 ing the sphenoid, represents the simplest form of the crystal- 

 lized mineral. 



It is interesting to note that this form differs very slightly 

 from the isometric dodecahedron. This similarity is accounted 

 for by the axial ratio of the mineral, 1 : 0*98525. The resem- 

 blance of the crystal to the dodecahedron is well brought out by 

 comparing it with a model of the same. In the drawing and 

 in the crystal itself, the illusion is destroyed by the downward 

 extension of the prism plane. 



The crystal is unusually large for the species, having an aver- 

 age diameter of four centimeters. The largest of the Chester 

 County crystals had diameters of a centimeter. Lacroix men- 

 tions large crystals from Oued Allelah of Algeria, Africa, hav- 

 ing diameters of eight millimeters. The rather indistinct 

 sphenoids from Ellenville, 1ST. Y., have about the same dimen- 

 sions as the Somerville crystal. 



Credit is due to Prof. Palache for assistance in the examina- 

 tion of the specimen and suggestions in regard to its importance. 



Tufts College, Massachusetts, 1904. 



