20 



mitive facets at 1 . 1 . A little rounding face on the acute 

 angles of the broader planes of the pyramid towards the fa- 

 cets of the prism, fig. 4, alters the parallelism of the edges, so 

 that by turning round the two halves, as in the next figure, 

 is formed the puzzling appearance so proper to be cleared up, 

 on account of being totally new in Crystallography, and 

 extremely curious. 



This noble, beautiful, and singular Crystal is from Derby- 

 shire, and is so suitable to precede the nextfigure, that I 

 thought it quite proper to place it here, though indeed it is 

 only the metastatic formation, as in tab. 35 ; but the 

 breadth of two of the faces would disguise it to many, 

 and more so if mackled as in the next figures, with the two 

 faces still broader, and which this happily serves so clearly 

 to elucidate, and, by the illinitions of the fractures, helps, 

 to point out the mutual base of the mackling parts ; which 

 is, I believe, both new and extraordinary, as it coincides 

 with a plane drawn through the longer diagonal of the 

 primitive rhomb. 



Its colour seems clearly to depend upon the Oxide of 

 Iron, which is partly mixed and partly chemically com- 

 uined. 



