Steel and Iron 



433 



The following table adapted from tables prepared by Professor 

 F. W. Clark, published in Bulletin 491, United States Geological 

 Survey, pages 32-34, shows the relative amounts by weight in 

 per cent of some of the more important elements of the average 

 composition of the earth's rock crust. The table may be 

 profitably studied, and made to show by a little ingenuity the 

 relative abundance of the important metals; for example, 

 taking the natural occurrence of gold as 1, silver would be 20, 

 lead 4000, and iron 8,800,000. Compare with table on page 425. 



Pure metallic iron is rarely found in nature, unless it comes to 

 earth from interplanetary space, as meteorites, some of which 

 are practically pure iron. In the American Museum of Natural 

 History at New York City there is a collection of meteorites 

 of almost pure iron, brought from Greenland. One weighing 

 36^ tons is composed of about 91.5 per cent iron, 8 per cent 

 nickel, and .5 per cent cobalt. 



208. Kinds of ores. Iron in plentiful and workable quanti- 

 ties is usually combined with oxygen, carbon, or sulfur. With 

 oxygen it forms an iron oxid ore; with carbon and oxygen, an 

 iron carbonate ore; and with sulfur, an iron sulfid ore, or iron 

 pyrites. The iron sulfids are useful to-day not for their iron 

 content, but for their sulfur, which is used in manufacturing 

 sulfuric acid. The iron -carbonates are important ores in 

 England, but they form a very small part of the iron industry 

 2r 



