THE NATURAL HISTORY SURVEY. 2$ 



Pyrite. FeS s . Regular. 



It occurs both in the drift and in the native limestone of 

 the region. In the drift it is the most usual form of the iron 

 sulphide, whereas in the limestone marcasite, the orthorhombic 

 form, predominates. The fitness of the name pyrite becomes 

 evident when a specimen is struck with steel or flint, for bril- 

 liant sparks are given off. It is called iron pyrites to distin- 

 guish it from other forms of pyrites such as arsenical p. and 

 copper p. 



The pyritohedron (210), the most common form, is repre- 

 sented in Fig. 2. In all the specimens examined the faces 

 have been striated, at times indistinctly, at other times in a 

 pronounced manner. As far as observed on these specimens, 

 the striations have been in the directions indicated in the figure, 

 and never at right angles to this direction as is reported by 

 Lacroix as occurring in French minerals. Usually the pyrito- 



Fig. 2. 



Fig. 3- 



Fig. 4. 



hedral faces are repeated until varying degrees of distortion 

 result. Fig. 3 represents the building up of the planes in a 

 crystal about one-eighth of an inch in diameter, until the front 

 surface is flat and the other planes have nearly lost their 

 resemblance to a pyritohedron. In Fig. 4 the operation has 

 been carried so far that a cube has resulted. These pseudo- 

 cubes are so common that in all the samples examined the 

 cubical faces are strongly striated and the edges truncated with 

 pyritohedral planes. PI. IV, fig. 2 represents examples from 

 the Niagara limestone. In the left hand specimen are a group 

 of such cubes, disclosed after the original calcite covering has 

 been dissolved with hydrochloric acid. The largest crystal on 

 the right side of this specimen is that represented in Fig. 4. 

 In the right hand specimen the calcite is left remaining. This 

 occurrence suggests that the iron sulphide is more apt to crys- 

 tallize in the regular system when the solution from which it is 

 formed is pure. When the solution is contaminated with for- 



