sosman: problems of the oxides of iron 69 



solution are yet to be investigated. It is not certain, even, what 

 compounds of iron were originally present. The natural sus- 

 spicion is that the iron was present as chlorides or fluorides, 

 since these compounds are known to be volatile at comparatively 

 Low temperatures. Many geologists have objected that in 

 some cases the associated rocks show no trace of alteration by 

 pneumatolytic action, or contain little or none of the element 

 supposed to have been combined with the iron. The Kiruna 

 magnetite ore-body of Sweden, for instance, shows sharp con- 

 tacts against unaltered normal prophyries. But in the face of a 

 phenomenon such as that seen at Kilauea, where vast quantities 

 of sulfur and its compounds are given off from the lava lake, 

 Leaving hardly a trace of sulfide of any kind in the solidified 

 lava around the crater, we need not feel discouraged about pro- 

 ceeding with experiments on the deposition of iron oxides from 

 those compounds which are readily volatile and on which the 

 basic data of temperature and concentration, at least, are 

 obtainable. 



One set of facts regarding hematite deposits of the magmatic- 

 pneumatolytic type is to be noted at this point, namely, their 

 magnetic properties and their content of ferrous iron. We have 

 found by some preliminary, as yet unpublished, measurements 

 that the force exerted upon a solid solution of Fe 3 4 in Fe 2 3 

 by a non-uniform magnetic field is roughly proportional to the 

 percentage of FeO. This holds true for both artificial and natural 

 oxides, including even some martites high in ferrous iron. On 

 the other hand, oxides containing ferrous iron (perhaps as 

 carbonate or as other compounds), but in which the FeO is 

 not in solid solution, such as the limonite from Mt. Ktaadn, 

 Maine, have a much lower susceptibility than the corresponding 

 solid solution. 



Again, an oxide formed by the oxidation of precipitated mag- 

 netite, as has been mentioned above, may have a very high 

 susceptibility, although the percentage of FeO may be very small. 

 We have examined one such oxide found by Messrs. Graton and 

 Butler in a gossan deposit. Hilpert reports that examples have 

 been found in Europe in association with carbonate ores which 





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