160 



bright greenish yellow colour with a metallic lustre, and 

 the flaws tarnish to the various colours of what is commonly 

 called Peacock Copper Ore. The fracture is smoothish, 

 having more or less of a fine-grained surface, sometimes like 

 the finest sand, as count Bournon has observed. The 

 crystals are brittle, and too tender to strike fire with 

 steel. 



The left hand sides of the two figures show the inclination 

 to form three trapezoidal faces on the triangular ones; and 

 the figure between two columns of quartz shows them more 

 plainly, as it does also the signs of the triangular lamina? of 

 superposition. This is taken from another Cornish speci- 

 men. The geometrical figure shows the somewhat obtuse te- 

 traedron, each face of which is replaced by three trapezoidal 

 ones, making a dodecaedron. The nearest modification to 

 this kind is in Rome de ITsle, tab. 1. fig. 28. but this has 

 twelve additional isosceles triangular faces. Haiiy has a crys- 

 tal something like this in sulphuret of zinc, which he derives 

 from the rhomboidal dodecaedron. See his fig. 197. The 

 rounded tetraedral crystals are therefore passing to the 

 dodecaedron, in an almost imperceptible manner, as the 

 three figures on the second line show. This specimen has 

 some more perfectly marked, and some truncated like the 

 two left-hand figures. 



