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. Fuel 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. Xo granite, sandstone, slate, or limestone, contain- 

 ing it, is fit for architectural purposes or for any outdoor 

 uses. The 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 munrfic of miners. 



Marcasite or White iron pyrites. This ore has the same composition as 

 pyrites, but differs in crystallizing in trimetic forms. I/\I=1W 36 ". 

 The color is a little paler than that of pyrite. and it is more liable to 

 decomposition ; hardness the same ; specific gravity 4'6-4'85. 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, X. Y. Massive varie- 

 ties are met with at Cummington, Mass. ; Monroe, Trumbull, and 

 East Haddam, Conn. ; and at Haverhill, X. H. 



Pyrrhotite. — Magnetic Pyrites. Iron Sulphide. 



Hexagonal. Occurs occasionally in hexagonal prisms, 

 which are often tabular ; generally massive. 



Color between bronze-vellow 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.*S 8 = Sulphur 39*5, iron 60*5. 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 



