CHAPTER XXX 

 SILICON; BORON 



SILICON belongs to the carbon family, being, like carbon, 

 quadrivalent and non-metallic. 



Although silicon does not occur free in nature, yet its com- 

 pounds are so plentiful that about 26 per cent of the terrestrial 

 globe is silicon. Instead of naming all the rocks which contain 

 it, such as sandstone, basalt, granite, and so forth, it is easier 

 to say that limestone is the only common rock which is not siliceous. 



Silicon Si. The element is now manufactured at Niagara 

 Falls and elsewhere, by heating sand (Si0 2 ) with coke in an elec- 

 tric furnace. The process closely resembles that for making 

 carborundum (p. 333), except that less coke is used: 



2C + Si0 2 -r 2CO t + Si. 



The element, as prepared in this way, is a grey, crystalline 

 material. 



Silicon Dioxide SiOz (Silica), Physical Properties. Color- 

 less rock-crystal, often showing large hexagonal crystals, is pure 

 silicon dioxide, deposited from natural solutions. When im- 

 purities enter into it, smoky quartz, rose quartz (pink), and 

 amethyst (violet) are formed. Often the impurity changes dur- 

 ing the growth of the deposit, and beautifully variegated spe- 

 cimens, like jasper, catseye, and agate are produced. Chalcedony, 

 opal, and flint contain a small amount of water in combination. 

 The nodules (rounded masses) of flint break in splinters, when 

 struck, and our prehistoric ancestors dexterously fashioned their 

 implements and weapons from this material. The solid struc- 

 ture of sponges and diatoms is also hydrated silicon dioxide. 



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