174 DESCRIPTIONS OF MINERALS. 
porated, preparatory to its being run off into vats or troughs 
to crystallize. In other instances, the ore is coarsely broken 
up and piled in heaps and moistened. uel is sometimes 
used to commence the process, which afterwards the heat 
generated continues. Decomposition takes place as before, 
with the same result. Cabinet specimens of pyrite, espe- 
cially granular or amorphous masses, often undergo a spon- 
taneous change to the sulphate, particularly when the atmo- 
sphere is moist. 
Pyrite, owing to its tendency to oxidation, and its very 
general distribution in rocks of all kinds and ages, is one of 
the chief sources of the disintegration and destruction of 
rocks. No granite, sandstone, slate, or limestone, contain- 
ing it, is fit for architectural purposes or for any outdoor 
uses. ‘T'he same destructive effects come from pyrrhotite and 
marcasite, which also are widely diffused. 
The name pyrites is from the Greek pur, fire, because, as 
Pliny states, ‘‘there was much fire in it,” alluding to its 
striking fire with steel. This ore is the mundic of miners. 
Marcasite or White iron pyrites. This ore has the same composition as 
pyrites, but differs in crystallizing in trimetic forms. J, 7=106° 36. 
The color is a little paler than that of pyrite, and it is more liable to 
decomposition ; hardness the same; specific gravity 4°6-485. Radi- 
ated pyrites, Hepatic pyrites, Cockscomb pyrites (alluding to its crested 
shapes), and Spear pyrites, are names of some of its varieties. It oc- 
curs in crystals at Warwick and Phillipstown, N. Y. Massive varic- 
ties are met with at Cummington, Mass.; Monroe, Trumbull, and 
East Haddam, Conn.; and at Haverhill, N. H. 
Pyrrhotite.—Magnetic Pyrites. Iron Sulphide. 
Hexagonal. Occurs occasicnally in hexagonal prisms, 
which are often tabular; generally massive. 
Color between bronze-ysllow and copper-red ; streak dark 
grayish-black. Brittle H.=3°5-4:5. G.=4:4-4°65. 
Slightly attracted by the magnet. Liable to speedy tarnish. 
Composition. Fe, 8,=—Sulphur 39°5, iron 60°. It is 
often a valuable ore of nickel, containing sometimes 3 to 
5 per cent. of this metal. B.B. on charcoal in the outer 
flame it is converted into red oxide of iron. In the inner 
flame it fuses and glows, and affords a black globule which 
is magnetic, and has a yellowish color on a surface of frac- 
ture. 
Diff. Its inferior hardness and shade of color, and its 
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