66 MINERALOGY. 
and fig. 22, a lump of crystallization of iron pyrites, like the preceding, 
drawn from nature. The crystals of pyrites which here appear in the 
simplest shapes of the regular system, exhibit other more complicated forms, 
as seen in pl. 33, figs. 33, 35, 41, 50, 54, 57,60. The crystals as well as 
the amorphous masses, have a light brassy-yellow color. A remarkable 
variety of iron pyrites, which is of a whitish yellow color, and more easily 
decomposed by the air than the preceding, is the water pyrites. It is not 
different from the other in chemical composition, but crystallized in another 
system, namely, the trimetric. 
Iron pyrites is a very useful mineral, although not applicable as an iron 
ore. It is rather used to furnish sulphur, and, in many places, the gold 
which is combined with it in small quantities pays well for its extraction. 
The pyrites is roasted, and the iron burnt to an oxyde, the sulphur to 
sulphuric acid. On leaching the mass, sulphate of iron is obtained, a salt 
of extensive application in the arts, under the name of green vitriol, or 
copperas. From the roasted green vitriol, fuming sulphuric acid, or the 
Nordhausen acid, is obtained. The residuum of oxyde is known in 
commerce as colcothar, and is used for coloring or polishing. Iron pyrites 
strikes fire with steel; and has, in certain cases, replaced flint for this 
purpose. | 
5. Molybdenite, or Sulphuret of Molybdena. 
This is exhibited in foliated masses, composed of very thin, bluish grey, 
metalloid plates, unctuous to the touch like graphite. It occurs imbedded 
in granite and gneiss, in Sweden, Silesia, Hungary, France, Switzerland, 
the United States, and other places. It is found, generally, in the shape of 
bent leaves, between the constituents of granite, as shown in pi. 33, fig. 23. 
The metal forming the basis of this mineral has some very peculiar oxydes 
and salts, which are distinguished by their beautiful color, and are used by 
painters. 
6. Arsenical Pyrites. 
This mineral is distinguished for its remarkable crystalline forms. It is 
of a silvery white color, uneven fracture, and also occurs amorphous, 
granular, or homogeneous. On being heated it gives off metallic arsenic, 
leaving behind simple sulphuret of iron ; for this reason it is very useful for 
the production of arsenic. It sometimes contains small quantities of silver 
and gold. The crystals of this mineral are rectangular octahedrons, single 
individuals often occurring of great perfection sprinkled in the general mass, 
as shown in jig. 18. It is found in beds and veins, in the primitive rocks, 
at Freiberg, the Hartz, in Bohemia, Cornwall, Sweden, and Hungary. 
7. Grey Copper Ore. 
Besides the preceding simple sulphurets, there are still a large number of 
more complicated combinations; among which this ore, or fahlerz, is 
conspicuous. This may be considered as a sulphuret of antimony, copper, 
and iron; in which combination, however, the antimony is sometimes 
partially or entirely replaced by arsenic, the iron by zinc, and in another 
variety by mercury: in the argentiferous ore, for the iron and_ copper, 
silver is partly substituted. This ore is sometimes found in remarkable 
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