sosman: problems of the oxides of iron 67 



A2 and the A3 inversions, further confirming the view expressed 

 above, that these inversions are intra-atomic. Further light 

 could be obtained on the problem by a comparison of the struc- 

 tures of the magnetic and the non-magnetic forms of Fe 2 3 . 



This apparent dependence of magnetic properties upon the 

 arrangement of the iron atoms in space opens up interesting 

 possibilities. If magnetite can be oxidized to ferric oxide without 

 loss of its magnetism, it may be possible to convert it into other 

 compounds, or even to convert metallic iron into compounds of 

 iron, in which the arrangement of iron atoms will remain un- 

 disturbed. A highly magnetic compound of iron with a high 

 electrical resistance, for example, might possess industrial as 

 well as academic interest. 



Having barely touched upon some of the problems in chemistry 

 and physics that are raised or partially solved by the study of the 

 oxides of iron, I wish to devote the little time that remains at my 

 disposal to the consideration of a few of the geological problems 

 connected with these oxides. 



THE OXIDES OF IRON AS RELATED TO CERTAIN GEOLOGICAL 



PROBLEMS 



The oxides of iron rank high among the earth's important 

 minerals, since metallic iron is manufactured almost exclusively 

 from oxide ores. 23 Questions of genesis of the ores of iron there- 

 fore furnish topics of perennial interest to the economic geologist. 

 The widespread occurrence of these ores makes them also of 

 interest to the student of historical and structural geology. 



At the present time the so-called magmatic and pneumatolytic 

 ores are attracting the most attention from a scientific standpoint, 

 though economically they are secondary in importance to the 

 sedimentary and residual ores. The magmatic-pneumatolytic 

 ores range in composition all the way from magnetite to hematite. 

 Two different modes of origin account for them. Certain large 

 magnetite deposits are claimed to have been deposited in the 

 lower portion of large igneous masses by gravitative settling 

 of magnetite crystals while the mass was still molten. This 



23 Carbonate ore formed only 0.006 per cent of the production in the United 

 States in 1915. (E. F. Burchard.) 



