DESCRIPTIVE CATALOGUE OF COLLECTIONS IN ECONOMIC GEOLOGY 

 AND METALLURGY IN THE U. S. NATIONAL MUSEUM. 



By Frederic P. Dewey. 



INTRODUCTION. 



The systematic collections in economic geology and metallurgy are 

 designed to show the actual occurrence of each metal and the pro- 

 cesses used in their extraction ; to these are added illustrations of the 

 occurrences of non-metallic ores and their utilization. The systematic 

 collections should be carefully distinguished from the geographical 

 collection. 



The collections start in the case of each metal by showing the series 

 of minerals in which the metal forms an important constituent. The 

 specimens are selected to show each mineral in its best perfection in 

 order that it may be seen just how the metals occur in the ores. 



The next step is a series of ores selected to show the actually occur- 

 ring material that is mined, together with the associates of the ore. In 

 the case of the base metals there may not be much difference between 

 the ore specimens and the mineral specimens, except the greater purity 

 and perfection of the latter, and that an ore may contain several min- 

 erals of the same or even different metals, especially alternation prod- 

 ucts, which do not have a definite composition. 



In the case of the precious metals, however, there may be a wide 

 difference between the two, depending upon the manner of occurrence 

 of the valuable portion of the ore. In the case of silver, one part dis- 

 tributed through a thousand parts of foreign material jnav constitute 

 a paying ore ; if, now, this one part be distributed through the remainder 

 more or less evenly, it will not be possible to detect any silver mineral 

 m the ore. If, however, tlie silver should be concentrated into separate 

 portions tlirough the mass, it might be possible to pick out distinct- 

 ively silver minerals. 



The same observations apply to gold, but in a much greater degree 

 since gold is so much more valuable, and in sonic cases can be extracted 

 at much less expense than silver. This is especially the case with the hy- 

 9110— No. 42 1 I 



