MINERALOGY, 31 



guished by its lustre, and the property of being attracted by the magnet 

 in small particles, whence it is called magnetic pyrites. A large deposit 

 of pyrrhotite occurs at Croydon, where there is a vein of the sulphurets 

 of iron and zinc, ha\^ing a width of several feet, two feet of the thickness 

 of which is occupied by a very solid, compact pure pyrrhotite, and nearly 

 two feet more by a less compact variety. It is also found in considera- 

 ble quantity in Enfield, Orford, Haverhill, East Hanover, Lyman, Graf- 

 ton, and at Mt. Misery. Small deposits are found almost everywhere. At 

 Copperas hill, in Vermont, it is utilized in the manufacture of copperas. 

 Dr. Jackson mentions that the Franconia Iron Company attempted to 

 work the magnetic iron ore of Landaff, but that they failed to extract 

 good iron on account of the large amount of magnetic pyrites that the 

 ore contained, for sulphur in iron ore is very deleterious. 



When pyrrhotite is present in a section of a rock prepared for micro- 

 scopic examination, it can be detected by shutting off the light which is 

 transmitted through the section from below, and examining it by the 

 light reflected from the surface of the section. Pyrrhotite, being a me- 

 tallic mineral, will then appear bright in the dark field of the microscope, 

 and can be recognized by its bronze color. Sometimes a httle micro- 

 scopic grain in our dioritic rocks will be partly pyrite, partly pyrrhotite, 

 and partly magnetite ; and their lustres are brought into sharp contrast 

 in the field of the microscope. 



Sulphide of iron is commonly a very deleterious ingredient of building 

 stones ; but the magnetic pyrites does not decompose so readily as ordi- 

 nary pyrites. I have seen some gneiss from our state, in buildings, and 

 though the stone was sprinkled with particles of magnetic pyrites, it had 

 not become stained by long exposure to the weather. 



Pyrrhotite, in certain localities, contains such a percentage of nickel 

 and cobalt that it forms a valuable ore of these metals. I have exam- 

 ined some of the pyrrhotites of the state, and, although by a careful test 

 nickel was detected in them, I have as yet seen none that would be con- 

 sidered as an ore of that metal. 



i6. Pyrite [Fe, S.,]. 



Iron pyrites is another mineral that is very common, both in masses 

 and as a constituent of the rocks. It forms a large proportion of the 



