4CO PHYSIOGRAPHY. CLASS ir. 



NEU, which comprehends the hexahedral and the prismatic 

 Iron-pyrites, only the Common Iron-pyrites belongs entirely 

 to the present species : the remaining subspecies belong to 

 the following one, except the Cellular Pyrites^ which is com- 

 mon to both. In regard to the latter, it is necessary to ob- 

 serve, that if the small individuals lining the inside of the 

 cellular walls, which .themselves consist of rhombohedral 

 Quartz, are hexahedral Iron-pyrites, the varieties must 

 be referred to the present species, while they enter with- 

 in the limits of the following one, if these individuals 

 possess a prismatic form. The cellular shape is owing to 

 the form, of hexahedrai Lead-glance, in the fissures of 

 which, parallel to the cleavage, thin films of quartz have 

 been deposited ; and as a shape which is foreign to the es- 

 sence of either hexahedral or prismatic Iron-pyrites, it can 

 have no influence on tbe determination of the species. 



2. The hexahedral Iron-pyrites consists, according, to 

 HATCUE.TTJ of 



Iron 47'30 47*85. 



Sulphur 52-70 52-15. 



It is considered by BERZEI.IUS to be Fe S 4 , in which the- 

 proportion of iron and sulphur is = 45-74 : 54-26. In the 

 oxidating ffame of the blowpipe it becomes red upon char- 

 coal, the sulphur is driven off, and oxide of iron remains. 

 At a high temperature in the interior flame it melts into- 

 a globule, which continues red-hot for a short time when 

 removed from the blast, and possesses, after cooling, a 

 crystalline fracture and" metallic appearance. In heated 

 nitric acid it is partly soluble, and leaves a whitish residue. 

 Some varieties are subject to decomposition, when exposed 

 to the action of the atmosphere. 



3. Hexahedral Iron-pyrites is a very common mineral, 

 and occurs in various repositories. It is engaged in im- 

 bedded crystals, and in massive nodules in several rocks, 

 the first particularly in clay-slate and greywacke-slate, 

 the second in greenstone and other rocks allied to it, in 

 granular limestone, &c. It constitutes beds by itself in- 

 cluded in primitive slate, accompanied by rhonibohedral 



