MICA AND THE MICA MINES. 655 



of two elements, the gas oxygen and the hard, light, non-metal 

 silicon. It is a substance that is almost omnipresent in the rocks 

 of the world. In organisms, on the other hand, it is the carbon 

 which is the chief element, and about which the hydrogen and 

 oxygen and nitrogen group themselves. Silicon seems, then, to 

 play much the same role in the mineral world that carbon does in 

 the organic. In many respects the two elements themselves are 

 similar. But the point of interest lies in their compounds. Fine, 

 crystallized carbon, the diamond, is not readily altered. Nor are 

 its simpler compounds with the elementary gases, such as carbon 

 dioxide, marsh-gas, and cyanogen. But when the compounds be- 

 come more complex, when carbon unites with all three of these 

 elements, and the molecule contains many so-called atoms, it is 

 correspondingly unstable. The highest development of this com- 

 plicated organic structure is found in the human brain, and in 

 the rapid changes which go on in these tissues we have, if not 

 the cause of thought, at least its accompaniment. The quality 

 and quantity of thought apparently depend upon the differentia- 

 tion of these carbon compounds, and the consequent ease and 

 rapidity with which they can decompose and recompose. 



Now, we have in the mineral world at least a partial parallel 

 to this general behavior, and one that is well illustrated in the 

 members of the mica family. Silicon itself is never found alone, 

 and the proximate reason for this is readily understood. It is a 

 fundamental law of chemistry that, when two reactions are possi- 

 ble, that one will take place which will liberate the greater amount 

 of heat. Apply this to silicon. When it unites with oxygen, 

 the heat of combination is very great, greater than that produced 

 by the combination of oxygen with carbon, and consequently this 

 reaction would take place in preference to many others, even in 

 preference to the oxidation of carbon. The point is admirably 

 illustrated by the chemical reactions taking place in the Bessemer- 

 steel process. The pig iron which is run into the converter con- 

 sists in the main of metallic iron combined with carbon and sili- 

 con. When the blast of air bubbles through the molten metal, 

 it is the silicon which first oxidizes. The flame escaping from the 

 mouth of the converter is small and intensely hot. The spectro- 

 scope shows a predominance of the silicon lines. Then the carbon 

 flame appears, less hot and more voluminous the second choice 

 of the oxygen. Finally, the iron itself begins to burn and the 

 blast is discontinued. Bearing these facts in mind, we would 

 never expect to find free silicon, and we are never disappointed. 

 When the element combines with oxygen, in silica or quartz, we 

 have a simple and extremely stable compound, as with the cor- 

 responding carbon compound. At a high heat and in the presence 

 of metallic bases, the silica will readily enter into new combina- 



