ON PYRITE AND MARCASITE. 
By If. X. Stokes. 
The object of this paper is to describe a chemical method by which 
the native forms of iron disulphide may be distinguished with cer- 
tainty, and by which their relative amounts in mixtures of the two 
may be quantitatively determined. The method is applied to various 
supposed pyrites and marcasites, and it is shown thai in the absence 
of well-marked crystallographic features it is extremely easy even for 
experts to be deceived as to the nature of a given specimen. 
I. UNCERTAINTY OF METHODS OF DISTINGUISHING PYRITE 
AND MARCASITE. 
Pyrite and marcasite are usually distinguished by their differences 
of crystalline form, color, density, and ease of oxidation. 
CRYSTALLINE FORM. 
Pyrite usually crystallizes in cubes, often in pentagondodecahedrons 
or octahedrons, and frequently in combinations of these and more 
complicated forms of the isometric system, while marcasite assumes 
various forms of the orthorhombic system. This criterion is inappli- 
cable when the minerals assume the massive or compact form, or 
when they occur as concretionary nodules in which the crystalline 
form can not be made out. .Moreover, pseudomorphs are not uncom- 
mon, and paramorphs of pyrite after marcasite and of marcasite after 
pyrite are said to occur, in which events no conclusion can be drawn 
from this source. 
COLOR. 
The color of pyrite is generally said to be pale brass yellow, while 
that of marcasite is described as tin white, grayish white, greenish, 
brass yellow, bronze yellow, and in other terms. Dana ! describes 
1 System of Mineralogy, tith ed., p. 94. For a list of terms and references see Julien, Annals 
New York Acad. Sci., Vol. IV, 1887, p. 179. 
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