355 



TAB, CCCLXXXIIL 



FERRUM sulphureum. 

 Sulphur et of Iron — Iron Pyrites. 



Div. 1. Crystallized. 



X lates. 366 and 367 are curious examples of the crystalli- 

 zation of this substance. The present extraordinary speci- 

 men seems to elucidate somewhat of the origin of those 

 modifications from the cube. See the right hand lower figure. 

 Two of the horizontal edges at each end -of the cube are 

 replaced by rounding faces of such extent that they meet 

 each other in a line, towards which the vertical faces arc 

 enlarged at the same time that they become concave (see 

 the right hand figure) : three of these crystals are grouped 

 together to form the left hand figure, thus disguising the 

 cubic structure. These and various other intermediate forms, 

 depending upon such a process, are on the specimen, that is 

 to say, one independent crystal, another notched, or one 

 joined as it were by one of its concave sides to another or two 

 others, not more, with the mutual loss to each of a concave 

 face, forming a straight seam, while the other sides are more 

 or less concave or straight, same as represented in the figure, 

 with the striae of aggregation on the upper part, as I shall 

 call it for distinction sake; the whole appearing as if formed 

 from a centre into three wedges. The crystals on this spe- 

 cimen are remarkable for their thickness, which much faci- 

 litates the study of them : as they become thinner, they 



