161 



TAB. LXXVIII. 



We continue this modification with a very curious va- 

 riety of the same substance, probably less rich in copper, 

 although differing very little in the lustre or colour of the 

 fresh fracture. 



The outward aspect resembles the grey or vitreous copper 

 ores, being of a dull grey colour, and very roughly formed, 

 as it were of certain nuclei, which viewed in the direction of 

 the solid points, or angles, give a peculiar bright shining 

 glare. Its faces are more determined and flatter than in 

 the last : the three trapezoidal ones of the same are not 

 finished (see the right-hand middle figure), but leave a tri- 

 angular face, transverse to the original face of the tetrae- 

 dron, forming one equilateral and three isosceles triangular 

 faces on each side, which makes altogether a new sixteen- 

 sided figure. This is a modification very different from any 

 before mentioned. Haiiy only finds the modification from 

 the bevelling of the edges of the tetraedron, as in his grey 

 copper and copper pyrites, tab. 70 and 71, fig. 78 to 89° 

 However, the faces o on figs. 81, 85, 86, 87, 88, 89 ap- 

 proach it ; but the angle of incidence is that of the rhom- 

 boidal dodecaedron, or 120°; whereas ours is that of the 

 dodecaedron with isosceles triangular faces. Most of the 

 crystals in this group are truncated at the edges, Wkefig. 27 



