JR. W. Richards — New Habit for Chalcopyrite. 425 



Art. XL. — A New 



Habit for Chalcopyrite ; by R. "W. 

 Richards. 



A specimen of chalcopyrite collected in Somerville, Massa- 

 chusetts, by Prof. A. E. Dolbear, of Tufts College, some years 

 ago, shows apparently a new and simple habit for the species. 

 The specimen was found in a vein of rusty quartz in the quarry 

 between Broadway and Holland Streets, near Clarendon Hill. 

 The rock of the quarry is the so-called Cambridge or Somer- 

 yille Slate, referred by some geologists to the Carboniferous, by 

 others to the Lower Cambrian. This rock is a clay-slate cut by 

 many diabase dikes, which in turn are cut by numerous veins 

 carrying a great variety of minerals, among which quartz, 

 calcite, albite, prehnite, babingtonite, erythrite, chlorite and 

 oxides of titanium, recently discovered by Prof . Charles Palache, 

 of Harvard University, may be mentioned. 



The crystallization of chalcopyrite is tetragonal, and a sphenoi- 

 dal habit usually predominates. Prof. S. L. Penneld, in his 

 paper in this Journal on crystals from Chester Co., Pa. 

 (vol. xl, 207, 1890), figured specimens 

 showing prismatic and pyramidal 

 planes, and others showing sphenoid 

 and scalenohedral faces, which he sug- 

 gests may represent a prism and a 

 second order pyramid distorted by 

 oscillatory combination with the posi- 

 tive sphenoid. The indices he assumes 

 for the distorted forms agree with the 

 forms found on the crystal described 

 in this note. 



The Somerville specimen is shown 

 in the cut and possesses only two forms, 

 a prism m and a second-order pyramid 

 e. These have the indices 110 and 101, respectively, and present 

 the identical faces figured by Prof. Penneld, in a twin crys- 

 tal (1. c. fig. 8, p. 210). The rough character of the Somerville 

 crystal permitted only contact measurements and the best 

 readings were selected by choice. The angles giving the most 

 satisfactory set of readings are those around the coign m to <?, 

 e to 0, and e to m. These angles are nearly equal and were 

 found by measurement to be about 60°. This satisfies the rela- 

 tion that should obtain between the planes of the prism and 

 those of the second-order pyramid, 



e to i 

 e to 





59° 

 63° 



30'5 ; 

 46-1'. 



