Till UKLATION OF MINERALS TO THE ELEMENTS 221 



The non-metallic elements sulphur and carbon occur in the uncom- 

 liinrtl state in nature in considerable quantities. 



Of the eighty established elements, oxygen far surpasses any 

 other in its wide distribution, forming one fifth of the atmos- 

 phere, eight ninths of the water, and from 45 to 50 per cent, of 

 the earth's crust. The results of careful calculations indicate 

 that the amount of oxygen is hardly equaled by all the other ele- 

 ment s t a ken together, or oxygen forms about 50 per cent, of the earth 

 as known by man. Oxygen enters the composition of a large num- 

 ber of minerals as an important factor. Of the other elements there 

 are seven, silicon, aluminium, iron, calcium, magnesium, sodium, and 

 potassium, in their order of abundance, each of which composes at 

 least 2 per cent, of the earth's crust, and they are universally dis- 

 trilmted. The above eight elements compose at least 97 per cent, 

 of the earth as known to man. Metals to which we have become 

 accustomed, through their use in our daily life, thinking of them as 

 common elements, as copper, lead, zinc, silver, or gold, occur only 

 in restricted localities; and owing to their commercial value 

 the minerals containing them have been mined, with a constant 

 accumulation of the metal reduced. Elements such as titanium, 

 thorium, cerium, tungsten, uranium, and molybdenum, which even 

 the chemist, in the past, considered very rare, are at the present 

 time becoming well known in the commercial world, from recently 

 discovered uses to which their properties adapt them. These 

 rare elements are important constituents of but comparatively few 

 minerals, and these are usually restricted to localities where many 

 of them occur associated together. 



Such localities are constantly being searched for by the pros- 

 pector, urged on by the constant demand and increase in price, 

 as several of these rare elements have been proven useful in the 

 production of special steels, in the manufacture of lighting man- 

 tles, and in incandescent lamp filaments. 



At the present time salts of some rare earths are being produced 

 by the ton as by-products, which had chemists wished to secure 

 in pound lots only, it would a few years ago have been impossible. 

 Of the most important elements the following list includes those 

 which are found in the earth's crust in amounts exceeding .02 

 per cent. : 



Oxygen 49.98 Sodium 2.28 Phosphorus .09 



Hlicon 27.21 Potassium 2.23 Manganese .07 



