CHAPTER VII 

 USEFUL METALS CONTINUED (GROUP III) 



IRON, ALUMINUM, CHROMIUM 

 Iron : Its Properties, Occurrence and Uses 



Properties. Iron, symbol Fe, is a lustrous white metal sus- 

 ceptible of a high polish. Native iron varies in color from steel 

 gray to iron black. Iron is strongly magnetic but loses this 

 property when highly heated. It is malleable and sectile. It 

 does not oxidize in dry air but in the presence of moist air con- 

 taining carbon dioxide it becomes coated with rust. The oxida- 

 tion is far more rapid after the film of the oxide has once formed 

 over the metal. Iron is soluble in the dilute mineral acids. The 

 metal crystallizes in the isometric system. The specific gravity 

 of native iron is 7.5, while that of the furnace product is 8.1. 

 Its melting point is between 1550 and 1600 C. Its atomic 

 weight is 55.85. 



Minerals and Ores. Next to aluminum, iron is the most abun- 

 dant of all the metals. The principal iron minerals are as follows : 



Native iron, Fe, 100 per cent. Fe. Often alloyed with cobalt, 

 nickel and copper. 



Pyrite, FeS 2 , 46.6 per cent. Fe. Commonly known as fools 

 gold, crystallizes in cubes, octahedrons and pyritohedrons. 



Marcasite, FeS 2 , 46.6 per cent. Fe. Occurs in orthorhombic 

 crystals radiating from a common center and in an aggregation 

 of crystals flattened into a crest-like form called cocks-comb 

 pyrite. 



Pyrrhotite, Fe n S n+ i. With plus or minus 61.6 per cent. Fe. 

 Commonly known as magnetic pyrite. 



Melanterite, FeS04,7H 2 O. A natural green vitriol. 



Coquimbite, Fe 2 (SO4)3,9H 2 O. A ferric sulphate of some com- 

 mercial significance in Chili. 



Siderite, FeCOs, 48.2 per cent. Fe. Often in rhombohedrons 

 with curved faces. 



188 



