STORKS.] 
PHYSICAL DIFFERENCES. 
13 
ing impurities), shows how illusive may be conclusions as to the 
relative amounts of pyrite and marcasite based on density alone: 
Densities of some specimens of pyrite and marcasite. 
No. of specimen. 
Density. 
Composition, chemically determined. 
5 ... 
3 . 
5.041 
5. 023 
4.987 
4.891 
4.886 
4.880 
4. 856 
L843 
4.819 
t.563 
100 per cent pyrite. 
100 per cent pyr te. 
83.5 per cent pyrite. 16.5 per cent mar- 
casite 
100 per cent marcasite. 
100 per cent marcasite. 
100 per cent marcasite. 
99.5 per cent pyrite. 
99.5 per cent pyrite. 
100 per cent pyrite. 
100 per cent pyrite. 
33 . 
7 
10 
12 
39 
30 
31 
17 
OXIDATION. 
While il is unquestionably true thai marcasite oxidizes more rap- 
idly than pyrite under the same conditions, a compact, well-crystallized 
marcasite can be kepi almosl indefinitely without any change further 
than a superficial tarnish, whereas finely divided or porous pyrite 
oxidizes with greal rapidity,and this fad has frequently caused pyrite 
to be mistaken for marcasite. 
The amount of oxidation depends upon the time during which the 
specimen has been exposed; upon the peculiar conditions under which 
il has occurred, such as exposure to dry or moisl air, or to water hold- 
ing oxygen or other oxidizing agents in solution; upon whether the 
oxidation products are removed; upon the surface exposed per unit of 
volume; and upon an oxidation factor characteristic of each mineral, 
but probably not more than three times greater for marcasite than 
for pyrite. It is obvious, therefore, that no trustworthy conclusion 
can be drawn in any case from vit rioli/at ion in t he absence of definite 
knowledge of these factors; and even when t lie eondit ions of time and 
exposure are identical, as when the specimens are kept side by side 
surface 
in the cabinet, it is necessary to know the - factor before rapid 
mass 
vitriolization justifies one in pronouncing a specimen to be marcasite. 
One of the most extreme cases of rapid vitriolization that I have seen 
is No. 21 (pp. 36-37), which consists of nodules of practically pure 
pyrite. Many of the rapidly vitriolizing specimens consist of mixtures 
of pyrite and marcasite, and apart from the porosity existing in such 
cases it is possible that an electrochemical action between the two 
