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CHAPTER III. 



THE MINERALS IMPORTANT AS ORES ; THE GANGUE MINERALS, 

 AND THE SOURCES WHENCE BOTH ARE DERIVED. 



1.03.01. The minerals which form the sources of the metals 

 are almost without exception included in the following compounds : 

 the sulphides, the related compounds of arsenic and antimony, ox- 

 ides and oxidized compounds such as hydrous oxides, carbonates, 

 sulphates, phosphates, and silicates, and one or two compounds of 

 chlorine. A few metals occur in the native state. All the other 

 mineral compounds such as a chromate or two, a bromide or iodide, 

 etc., are rarities. It may be said that nine tenths of the produc- 

 tive ores are sulphides, oxides, hydroxides, carbonates, and na- 

 tive metals. The ores of each metal are subsequently outlined 

 before its particular deposits are described. 



1.03.02. The most common gangue mineral is quartz, while in 

 less amount are found calcite, siderite, barite, fluorite, and in 

 places feldspar, pyroxene, hornblende, rhodonite, etc. The silicates 

 are chiefly present where the gangue is a rock and the ore is dis- 

 seminated through it. All the common rocks serve in this capaci- 

 ty in one place or another. 



1.03.03. Source of the Metals. The metallic contents of the 

 minerals which constitute ores must logically be referred to a 

 source, either in the igneous rocks or in the ocean. If the nebular 

 hypothesis expresses the truth, and it is the best formulation that 

 we have, all rocks, igneous, sedimentary, and metamorphic, must 

 be traced back to the original nebula. This, in cooling, afforded a 

 fused magma, which chilled and assumed a structure analogous to 

 the igneous rocks with which we are familiar. Igneous rocks must 

 thus necessarily be considered to have furnished by their erosion 

 and degradation the materials of the sedimentary rocks ; while 

 igneous and sedimentary have alike afforded the substances whose 

 alterations have produced the metamorphic rocks. It may also 

 be true that eruptive rocks, especially when basic, have been 



